It kind of depends for me, sometimes it's just for fun, sometimes it's my form evolving and creating holes, and sometimes it's multiple factors. I'll share two recent examples, the first of which is switching up my putting putters. I putted with Neutron Envys for a while, but got a Judge as my players pack disc this past May when I played in the Easter Seals Classic at the Hippodrome. I really liked the way the Judge felt in my hand, and was tired of waiting for Electron Envys. I started putting with the Judges and dug them, and also watched Feldberg's push putt clinic at the New Zealand Nationals, and so my putting has slowly evolved with the Judges and now I'm a much better putter than when I was using the Envys.
The other story is adding a Tesla to my lineup this weekend. I've been throwing a Saint for a while, and it's started breaking in, while my form has been getting better. So what was once my Stable-OS driver is now my Stable-US driver. I was down at the IDGC looking at discs, and they didn't have a PPD or a Convict, which were the two molds I was considering. However, I picked up a Tesla and really liked the way it felt in my hand, and after throwing it today it's definitely making the bag as the disc between my Firebird and Saint. I'm even considering replacing the Saint with a Wrath to get some separation between it and my CFD.
So really, changing my lineup up, for me, can be a lot of different things. I really like trying new discs, and as my form improves and discs started beating in, I start learning how to change my lineup up to maximize my game