The fact that you qualify funny puns as "bad" already tells me you lack a proper appreciation of the beauty of a well-formed pun. Puns aren't "yet funny;" they are the highest possible form of human expression. Other than Riverdance, maybe, or bears that can ride unicycles (I know, it's "human expression," but ask yourself: who trains the bears?).

Humor, as I've said before, is consistently ranked as one of the most powerful aphrodisiacs known to science. How else could you explain my typing this from under a pile of nude co-eds? It's gotten so I have to wear reinforced underwear when I do stand-up.

No one knows exactly why being funny gets dates so incredibly hot for you, but my theory would be:

1. It projects a sense of confidence, even though you may be slowly withering on the inside.
2. It puts them at ease. People don't usually assault you right after telling a knock knock joke. Although if they did, that would be the scariest thing ever.
3. It rewards them for going out with you. Laughter is enjoyable; making someone laugh just gives them a reason to be around you. The alternative is to give them a dollar every time they do something you approve of, but that often turns into prostitution pretty quickly.

Conversely, if you tell a BAD joke, you risk casting a pall of awkwardness over the moment, training those around you to not be around you again in the future. So to answer your question, I'd say making someone laugh on a date is always a plus, but sarcasm and bad puns aren't necessarily the best way to make someone laugh. Unless that person is eight years old, in which case you're a monster.

Deploy jokes with confidence or not at all, and keep your material fresh. If you've got the knack for cracking people up in conversation, you've got a universe of hotties waiting for you to lower their defenses. If you don't, do what I do...mention balls a lot on the Internet and see if that makes people think you're funny.