20% sounds good, right?
Don't forget the 20%ers of a $25 bill and stayed for 3.5 hours. They think they tipped well, but don't realize they actually just robbed their server of making more.
On average, guest time at a table is 45 minutes. The server "flips" tables all shift, & each rotation is treated the same as all for the same reason anyone who has a job. $$$.
Lets imagine a server on a night that has a 2top in their section & unfortunately gets these "3.5 hour" guests that leave $6 on a $30 tab. That server could have flipped that table 4 more times in that frame, & for simplicity lets assume they all left $6 on a $25 tab. The campers cost their server $24.
Maybe not to some, but that 24 bucks means a lot to these kids...