I got into building PCs in my early teens - not that I could afford anything at that time, but I was somehow involved in upgrading the family tower when I was... 12 or something when my older brother took all his parts out of it to build his own. That PC was definitely not SFF - a late 90s big tower (PSU on top, crazy tall, still quite narrow, had feet that stuck out to the side to not tip over) with an 800mHz AMD Duron in it. First own PC was at 16 or so, in a Thermaltake Xaser III mid tower. That PC broke at a point when I couldn't afford to replace or fix it, so I had a (terrible) laptop only until I could afford a new gaming system - which was the polar opposite of SFF. Crossfire Radeon 4850s, CM Stacker 830 (ironically, the Nvidia edition 'cause I liked the black-and-green color scheme), which is... not a small case. Think I had 9 or 10 120mm fans in there at one point, and at one time ran 3x 750GB HDDs in RAID 5 as a boot drive along with two or three more for storage. Thought it was cool for a while, but the size really wore me down. Kept that case despite being sick and tired of it for something like 6 years, when I moved to a Define R4 - again, couldn't afford a full system upgrade, so ATX was holding me back. About this time, I got my first ITX case when I built a HTPC/NAS in a Node 304 - still in use. When I could afford to upgrade my desktop's motherboard, I went ITX Ryzen in the R4, and finally moved to an NZXT H200i last year. Not technically SFF (26l IIRC) but the smallest that could fit my ATX PSU and the custom water loop needed for my whiny Fury X within my budget (though I really wanted a cerberus!). Would have gone smaller if the pump on the Fury X didn't bother me so much.
Now, I'm an SFF convert, full time. I'm tempted to move to a smaller case in time for my main PC (though I don't like the idea of ditching a perfectly good PSU, and I'd need to get a less power hungry GPU), currently planning to spin out the HTPC part of the living room combo build into an APU-powered Lazer3D HT5 build, and working on squeezing a GPU into a dumpster-dived Dell Optiplex SFF. Oh, and introducing my PC-building friends to the convenience of OTS SFF solutions like the Node 202. Don't see any reason to veer away from the SFF path - it's been a decent while since I had more than one expansion card in use, and SFF cooling and cases today are amazingly good. Times really have changed.