I tried it once but didn’t see the use of it, but I saw it recommended often and I can see why, because it is nice to sync notes with your phone, if you need it there. I personally am a fan of the suckless/KISS mentality and just use syncthing to sync my plain markdown notes between devices.

one thing that annoyed me, though, was that the markdown editor in joplin always inserted some weird blank lines or spacings. That might not be relevant or even obvious for someone who just uses the rich text formatting editor, but I mostly used the plain text editor and eventually asked myself what joplin is basically useful for in my use case, as I already had syncthing in place and I could just use any plain text editor of my choice. So for me the benefit of hierarchically structuring my notes was not worth the extra program on my computer/phone, especially considering that syncthing and vim/codium are programs specifically created for the use case that joplin tries to merge into a single product. But I might be an extreme case, as I have also replaced Nextcloud with Filebrowser and Syncthing, so take my words with a grain of salt.

TLDR: Joplin is a great program and I can recommend it, it is just not suited for fans of the KISS mentality.