I mean it makes you feel a bit more special? It definitely has more perks for the members residing in Japan as for instance currently, you have TA Summer Party and only the members can attend. For her regular concerts, TA gets to participate in the ticket lotteries first.
Sometimes there's a giveaway of some items like a piece of clothing ayu wore or sth.
There are monthly wallpapers if that's your thing and you can check them in the wallpaper section even without being a member, just to get the big size you need to log in
https://global-fc.net/teamayu/contents/wallpaper/
Sometimes tours have their own special pages where you can find pictures of fans before the venue, and those are forbidden from being reposted anywhere else, the setlist and some other things like events when members send a message which will appear randomly to other members (works only on mobile).
Additionally to those things, there are ayu blog entries written by her. These days most are in Japanese so you need to use some online translator but they do ok to a decent job with it. Some are translated by the team and presented in English.
For quite some time they have been updating Mura-ayu channel on a weekly basis with a variety of videos like backstage stuff, funny moments, behind the scene of music videos. You can find some in the download section to get the idea.
Q&A that can be found on the forum also comes from there.
Oh and there is an option to message ayu or TA staff, but obviously it's a one-way street haha and you can only hope she reads it.
I think that more or less covers it ^^