Why shouldn't you pump for 30 minutes?

Pardon me, but I'm curious about the advice you've mentioned. Could you please elaborate on why it's not advisable to 'pump' for 30 minutes? I've heard various opinions on this matter, but I'm keen to understand your perspective. Is it due to the potential risks involved? Or is it more related to the efficiency of such an action? I'd greatly appreciate if you could provide a detailed explanation in a way that's accessible and understandable for a layperson like me.