For example, someone hasn't given an answer I needed but provided some useful info.
Is it wrong to comment with "+1 for …"?
If your only intention (and text) is "Wow, I liked this": Yes, then it's certainly wrong.
If, on the other hand, you include why you liked it (e.g. "especial useful point: XXX, easily overlooked." – thus highlighting things others might miss), or even add to it (e.g. "Great answer! By the way, note also that …") – then it's perfectly fine.
In short: If your comment has nothing but "+1", it's usually bad – if it holds additional information, it should be good :)
Note that I kept this answer "generic", so it applies to all SE sites. In context of SR, you might slightly adjust the second paragraph: e.g. pointing out a feature the answerer missed but the OP might be interested in already justifies a comment ;)
As a moderator:
I don't delete them if they follow a "+1 because
<reason>" pattern. Those serve to praise a specific attribute of the answer, and could help someone coming from Google in the future.
If I I see a comment like:
"+1 great answer"
"+1 nailed it"
Etc., when I'm just looking around the site, I'll generally delete them on sight if they're more than about a week old. The only real value they serve is to compliment the author, and after a few days we can assume the author has seen it.
If I see it in the flag queue, I'll usually delete it right away. Often it's the author flagging these, so we can know they've seen it. Otherwise, they're almost always more than a few days old.
So, I delete "+1" comments if they don't have any specific information about why the recommendation is good.
If someone provides an answer with useful information, but it's not the answer you need, then thanking them for the answer and explaining what helped is always a nice gesture.
The situation may also provide a great opportunity to clarify your original question so that future answers may be more appropriate. Perhaps the person who already answered will modify their answer or craft another one.