rush

I agree...only sucky houses COB

In order to keep membership of all groups somewhat on par half of the sororities are able to COB be each semester. The half that is below the median chapter membership total. And those are not always top or bottom or in the middle sororities. And the groups are more equal than they have been in the past. Rushing as a sophomore you would probably get those same groups anyway unless you have a close relationship with very involved sorority members.
If you only know one or two members, and they are not very involved with their sorority it isn’t going to make a difference during formal fall rush.

“Not always top or bottom”. I’ll agree but what percentage of top houses are offering COB. Some houses don’t meet quota and others have members that drop for various reasons. Some out of the houses control. But let’s be honest the bulk of houses doing COB aren’t traditionally top tier.

“Top tier” is subjective. If someone is THAT particular where they end up, they need to talk to someone in that sorority about if they COB. We have at least one sorority whose nationals doesn’t allow them to COB.
In reality 6 or 7 sororities regularly end up in somebodies top-tier. And 6 end up eligible for COB. So there is your percentage.
COB is a real good option for sophomores and juniors who will be brutally cut in formal fall rush.
I am in a sorority that ends up on a superficial ranking. We do COB most semesters, but not every semester, and it has usually been a quiet process. More often than not someone with a lot friends inside. But we do COB.