There are some who have a veritable cornucopia of pipes, and there are some who only have one, and everything in between. It's whatever works for you, and whatever provides the most enjoyment. Pipe smoking is way too subjective a pastime to have any accounting for taste. Like most things.
I myself am a minimalist. Large amounts of possessions give me anxiety, and pipes are no exception--having 100 pipes, or 50, or even 20...I can practically feel my own blood pressure rising at the thought of it. Counting cobs, I have 8, and that's more than enough for me. I have three main pipes, a Savinelli Tortuga 614 faux Oom Paul (it's more of an extremely bent billiard) for aromatics, a Savinelli Bacco 321 bent author for anything with latakia in it, and a Stefano Santambrogio bent Rhodesian for everything else, which is VAs, burleys, VaBurs and VaPers. These pipes all have fairly large bowls, so I also have a "brother" pipe for each one, all of which have smaller bowls.
I separate these blends to avoid ghosting, but I'll put anything in the cobs. It took me a while to figure out a system that worked for me, but once I did, I was happy with it, and I intend to stick with it. Some people separate even more fastidiously, some less. Which brings my diatribe back full circle to the original point--it's all a matter of individual preference. The most commonly used acronym on here (and rightly so) is YMMV: Your Mileage May Vary.