In pure dollars leaving too much on the table is bad, but a nice IPO bump is free marketing for the company. A 20-30% bump means it'll lead in a bunch of news stories, and create some buzz around the company. Of course, this might be less important for a non-consumer oriented company.
A bump means people in the market are trading their shares with each other at 20-30% higher than what the company sold to the market for, that's what it means by money on the table. It's as if they sold for below market value. An IPO pop cannot immediately be turned into cash to spend, can't pay for ads with stock
