Pummeling can be dangerous because your opponent can always mash out (you're not the ICs lol). It is harder to mash out at high percents, so it is safer to pummel the higher percent your opponent it (or safer to pummel more). However, even if they don't mash out, pummeling still gives them time to DI perfectly. For these reasons, I normally do not pummel unless I am trying to raise their percentage enough to create a new option. For example, if I grab fox at 30%, I'll pummel once before upthrow so that uptilt will convert to regrab easier. The only other time I'll pummel (besides when it creates new options) is when my opponent is at a really high percent and I have no followups, so I take the extra damage pummel gives.