I can't speak for others but I will chime in with my decision making in bulking. Originally I was training purely for aesthetics, not to compete in PL. I bulked up to around 95-96kgs (210lbs or so) but wasn't in great shape. That was also about 9 months out from my wedding so I started dieting, eventually getting down to a self-measured body fat of around 7-8% @ 78kgs (175lbs). Looking back I think I was probably more like 10-12% but regardless I could see most abs and was lean by anyone's standards. During this cut two things changed in my training:
1. I got bored of lifting high reps and discovered a love of smashing heavy low rep sets.
2. I decided to compete in PL.
During my cut I used 5/3/1 and made good strength gains despite my diet. After the wedding though I knew I felt small and wanted to get bigger again. I was around 82kgs (180lbs) when I got married and decided to compete at 90kgs in my first push/pull meet. With the increased food intake my progress was much faster and I felt happier being bigger again.
After that meet in December 2010 I competed at 90kgs again 2 months later at the end of Jan and had to diet from 95.5kgs to 93kgs and then cut water to make weight. I hit my goal of qualifying for nationals but didn't leave much on the platform and with my daughter on the way, I decided to take a year out and go up a weight class so that I could maximise gains again and also not worry about dieting to maintain a weightclass. Also the winning totals in the 90 and 100kgs class are almost the same so why suffer.
I competed again in December at 102.5kgs (no weight classes at my gym meet so I didn't cut water) and put up a 77.5kgs PB total.
To summarise here are my gains over the last two years:
Jan 2010 (BW 85kgs and dieting) - SQ 130 (high) BP 100kgs x 2 (TnG) DL 160kgs (with straps and awful form)
Aug 2010 (BW around 80kgs just before wedding) - SQ 140kgs x 1 (to depth) BP 115kgs (TnG) DL 180kgs
Dec 2010 Push/Pull meet @90kgs BW - SQ 160kgs (training) BP 122.5kgs (meet commands) DL 200kgs (meet)
Jan 2011 Full Power Meet @ 90kgs BW - SQ 182.5kgs BP 132.5kgs DL 215kgs Total 530kgs
Dec 2011 Gym Full Meet @102.5kgs BW - SQ 227.5kgs BP 147.5kgs DL 232.5kgs Total 607.5kgs
So my decisions to gain weight and move to the 100kgs class were basically twofold:
1. Being bigger and not dieting constantly would make me stronger.
2. I like being big.
I feel as if I've waffled here but if you have any more specific questions, let me know