First off, there are many eras of BBS'ing. So you might get different responses based on the vintage of the respondee..

In the early-mid 90's, BBS's were still a subculture driven by word of mouth, particularly in the period before the web came to AOL. With BBS's, you came for the technology, but you stayed for the community. There was a huge technical barrier to entry for kids/teens that didn't have a mom/dad that could help them configure things like arcane AT commands for their specific make/model of modem, or explain the differences between things like the various download protocols (named things like "y modem-g" or "z modem"). Sysops took on a mentorship role and probably helped countless 90s teens get into tech.
I mention community because it's the most memorable value-add of BBS's. Something that's arguably been lost for most web & app users, but maybe still lives on in tight subreddits or Discord channels. I think there were 2 major drivers of the tight knit community on BBS's. First, due to the cost of long distance calls back then, the people that you were talking to were almost always from your same area/city. You weren't trolling someone on the other side of the world, but someone that could live in your neighborhood. Second, the barriers to entry were pretty high and it filtered out the userbase to mostly just geeks. You had to have a PC ($2-3k) with a modem, dedicated phone line (or an understanding family that didn't mind not making calls), and the luck to have a BBS in your area code that you'd even heard about. I wouldn't underestimate the latter point. Without the web or access to newsgroups, how I even heard about and got the number for a local BBS bewilders me. These were platforms run out of people's basements and didn't advertise through traditional channels.
One thing I just recalled was how payments worked. Running a BBS was expensive (paying for multiple phone lines, expensive hardware, and software licenses for the BBS application itself). You could usually mail cash to the sysop, but a major innovation was BBS's that provided a service where you'd call a 900 number that charged $20 to your phone bill and, when you called, would read off an access code that you'd redeem for "minutes" on the BBS. Huge.
One major use case for BBS's in this period was as download repositories for text files (tech, counterculture, even pirated software, etc). This sounds ridiculous now, but people were information starved back then compared to today. For BBS text files, imagine Wikipedia but way worse and way more bullshit. Still, it was incredible to get access to text files on BBS's. Porn wasn't a thing on the BBS I went to, but must've been out there.
Media files were usually low-res jpeg, gifs (not animated, just static images), and "ASCII art". Video was not possible in any form. A 28.8k modem might achieve 3 kilobytes per second of download speed and rates were sensitive to analog line noise (the wiring from your house to local branch made a difference).

Multiplayer gaming was also a major use case for BBS's during this time. Multiplayer FPS deathmatches on Doom & Descent were very popular and was mind blowing. Id software eventually offered an official dial-up service for FPS Doom multiplayer called Dwango, but it was very expensive and not in my area. For most BBS users, emulating a LAN over dialup was a compelling alternative to building an actual hardware LAN at your house.

Sorry for any typos -- I'm typing this on my phone. Happy to answer any questions about this long forgotten technology.