You have to look at what the grab offers and think accordingly.
- It has a lot of ending lag
- It has decent range (the animation is misleading, but it's still decent).
- It stays active for a long time so you can punish spot dodges (you shouldn't count on that, but it means people can randomly run into your grab, too).
- The further the opponent is, the longer it takes to grab him. If he's directly in front of you, it grabs immediately.
your dash grab will whiff at point blank...sigh.
I always miss it when going into a dash
It does miss, but only if you run into the other character before grabbing. If you press the grab button a few frames before hitting the other character, you will be able to perform a dash grab at (almost) point blank. It's really not hard to do, and doesn't noticeably limit your options, so it's hardly a relevant flaw.
By looking at this only, you see that it's a completely different grab from most of the other characters. Link's or Samus' grabs work in a similar way, and are probably the closest to Pac's.
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The pummel is strong. It's slow, but you can and should be using it to rack up damages. Grabbing alone means you have 3/6/9/any other multiple of 3 depending of the percent + minimum 5% from the throw, free damages. This is not negligible.
The throws are not that good, in the sense that the follow-ups are either non-existant, situational (depending on teching/DI from the opponent), or not worth it (either you don't do much damage/knockback and you're better off charging fruits, or it's unsafe if you miss). You don't really have any true combo you can abuse like other characters can *cough* Diddy ZSS *cough*. Don't get me wrong, I'm NOT saying you can't follow up form the throws, I'm just saying you can't do it as reliably as many other characters.
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- Dthrow (10%): Your go-to throw. If you don't have any reason to use the others, use this one. It's also the throw that gives you the most follow-up possibilities.
- Bthrow (11%): You can kill with it, but need rage, need the opponent at a high percent, and need him not to be too heavy. Still a kill option to keep in mind. It's the throw that does the most damage. You can Bthrow and try to Bair, which can kill early, so that's cool. And Pac is pretty good at gimping in general, them's the facts.
These are the two throws you want to use the most.
- Uthrow (5%): I don't really know the purpose of this one. You can Uthrow to Uair at early percents, I guess.
- Fthrow (6%): Like Bthrow, but worse. If you can't Bthrow use this one. I guess.
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Because of the drawbacks of the grab, and because Pac is not a combo-heavy character, you should be using the grab in only one situation: when you can. Your gameplan doesn't revolve around it; you have other effective ways to rack up damage (do not rely on Throw -> X aerial combos to do so), and don't need it to kill. This means you shouldn't fish for the grabs, but grab when it's safe to do so. If the opponent does a punishable thing, you can go for a grab (but a smash might be better if you can). Pac's grab's primary fonction is getting the opponent off you, and doing a bit of damage at the same time.