I know this thread has been dormant for a while and I understand that most people here are talking about NPC sororities and IFC fraternities, but I wanted to address the original comment that included NPHC groups.
I can only honestly talk about my sorority, Theta Nu Xi. We intentionally maintain small chapters.
http://www.thetanuxi.org/question4.html
I certainly believe that there are benefits with bigger chapters just as there are benefits with smaller ones. I think it really depends on what you are looking for. With big chapters, you have a lot of programming options and you can be very active with a lot of your sisters/brothers. But, with smaller chapters, you have a lot more freedom to choose the programming that your chapter will proceed with, whereas bigger chapters have to be pretty rigid so plans don't fall through.
And, bigger chapters can be great since you have sooo many people to get to know...you're bound to find someone you click with. In smaller chapters, you pretty much have to get along with everyone whether you like her/him or not...but I believe this teaches a good lesson.
We ALL have strong reasons why we picked our chapters, right???