It's an enjoyable thing to do. I don't like many things in the game but housing is one of the things I like. I'm always on top of the "hardcore" content in the game but FF14 just isn't my game. I play because my friends play and housing is a great place to socialize etc... So in those regards, it passes the time for me. When I redecorated the FC i'm part of 2 years ago, it was a big undertaking that took 1-2 weeks and 120mil gil~ish. It is a big gil sink but people before didn't care to go to the FC mansion but after everyone was going there regularly. It became a hangout hub and a to-go place for food bonuses before dungeons etc... New recruits loved it too and stayed, got an FC apartment and apartments often became an extension to the mansion as different "rooms".

There are perks beyond the "epeen" as what you would say. To some of us, it's just as important if not more important than end-game battle content.