One guideline says: You should add a space between a - and the following sentence.
For example: - Today is Wednesday.
The other one says: You should not add a space between a - and the following sentence.
For example; -Today is Wednesday.
So my question is: To space or not to space?
I would say put a space between the - and the next word. It’s a bit easier to read, too, IMO.
I thought about this issue a bit. I never put a space after the dash. Reasons: 1. norm on our (Croatian) public TV programmes; 2. without the space the following sentence looks more cohesive and separated from the previous one.
Example:
(-)Today is Thursday, right? -Today is Wednesday.
vs.
(-) Today is Thursday, right? - Today is Wednesday.
I consider the dash to be the beginning of the following sentence, indicating the change of speaker, not an equal separation between the two sentences.
I think the dash-space thing comes from books. There for the most part there is a space. But there, also, for each change of speaker there is a new line, which can’t be applied in subtitling.
Which leads me to another question. If dash indicates change of speaker, why put it in the beginning of a subtitle if the speaker hasn’t changed from the previous subtitle?
Example:
A: Tomorrow I have to go to the dentist.
A: Today is Thursday, right? B:-Today is Wednesday.
vs.
A: Tomorrow I have to go to the dentist.
A: -Today is Thursday, right? B:-Today is Wednesday.
Well, in the sub guideline I found, which was written for Dutch subtitlers, the rule is that you should only put a dash when there are two speakers in one segment and then you only should put one before the second speaker. And I always follow this rule, because I think it looks nicer and the first dash is unnecessary.
I like to put a space in between. It looks okay for the sample sentence because there’s a gap for capital T. But for another alphabet, it’ll be joined to the first, which I think makes it harder to read.
E.g.
-I like eating.
vs.
Besides, I sometimes put in the dash without the space to show when someone’s speech is interrupted. I should probably use the long dash, but I can’t type it on my keyboard, so I make do with the small one.
I can’t say for Dutch, but I usually put a dash in front of each dialogue when there’s two speakers in one segment, when I sub in English that is. Cause that’s usually in the guidelines for English subbing. And I also feel that if I were only to put a dash for the second speaker, then it might confuse me, especially if there’s no space in between the dash and the word. Cause in English, when a word is broken into two lines, it’s usually shown to be a word by placing a dash.
E.g.
I’ve been looking every-
where for you.
I know that when the word is broken up, the dash is usually put at the end of the first line, but it might still be confusing. So I think putting the - before every speaker makes more sense.
For the problem of a word broken in two lines, you can use < br > zodat the complete word goes to the second line. Becaue I read somewhere it’s easier to read subs when words and wordgroups belong together are written together.
E.g.
I’ve been looking
everywhere for you
I do it the same way moonandstars does.
You are refering to the dialog breaks dash space.
I see often people omit the second space and it’s difficult to read on the screen.
For example in this dialog:
I thought those additional italics were just bugs created by the system. I didn’t think people actually typed in multiple italic markers.
thanks for the clarification but they are not everywhere just somewhere, so where is the bug hidden 
It is easier to read the sub if the space is put in between the dialogue and the hyphen. I require the hyphen in front of the dialogue from each character if two are in the same segment.
But that still doesn’t explain why there would be multiple (like 3) end italics marks for one segment, unless if the coding for the automatic insertion is a bit screwy.
I saw this happening when people would initially put several < i > if, for example, in the same subtitle they had a lyric of a song and a piece of conversation. Also, some people don’t pay attention to “cleaning up” the subtitle from unnecessary styling codes.
this is an interesting revelation and would technically make sense if the characters are set by the program.
I understand that when using the italics it’s enough to use them only at the beginning as the program understands to form the italics just at < i > for some reason all my prior mods said it’s nice to close them, which is obviously more typing work, I in particular had issues on my american pc, whenever for unknown reason after clicking save, the characters would so often change to capital i (I) < /I > that would actually then show in the subs and I had to correct it. - As I sub now with my tablet, there are no autocorrect problems. -
So you are saying if there is only one line/sentence in italics only < i > is needed?
But in your example you put the sentences on the same line. Which doesn’t happen in subtitles, as we change line for the second speaker.
I think it’s much much neater this way.
Since both statements are short, yes, you would put them in two lines and then it is much neater with space, as you say. But if the first sentence was long, then I would follow our “rule”. I would avoid three or more lines at all cost, since they cover the screen too much, which is particularly important for smaller screens.
A lot of these things are just a matter of how you’re used them. I chose not to put one from the beginning, because that’s how we are used to it. But, as some already mentioned, non-romanic alphabets can look pretty bad without a space.
Additionally, having no space saves you the trouble of putting < br > when the dash is separated from the rest of the sentence falling into the second line, and it makes the sub that tiny (perhaps insignificant) bit shorter.