Except you don't get pets, valks, inv slots, etc, for just creating a regular character. Nor are you getting an extremely relaxed way to hit TET boss gear as a new or returning player. It used to be that Tuvala also offered decent fs stacking, back when the similarity with tet boss gear was also kinda reflected in the enhancement rates.

On top of that, if you're not a fan of just trash/hour, doing the MQ will give you extra skill points books that you don't get on normal servers. You'll have the option to skip the MQ entirely too and just go out and trash/hour (which, to my knowledge, is another thing you don't get when playing on a normal character). 

Let's also add that you have an easier time if you decide to take on the challenge of running the dungeons (boring, long, unrewarding, however you wanna tag'em).

Other than that, yeah. None. Granted, all the above (maybe minus the stuff you get for completing the pass) aren't so attractive when you're past 700gs and already have everything. Luckily though, seasons aren't aimed at those players, I don't think.

Oh, oh! Should we also add the fact that you can basically get 2 high level, high sp characters at the price of just leveling one in the "none" category?... Good answer, otherwise! :D

Attention New Players: 

There are Elvia servers (the ones with the green swirl) these are hard mode servers with better payout.

There are Season servers, for Season characters, no PVP allowed, level grinding a new character from 1 to 61 over the season.

There is one PvP server, I don't go there, never been there.  I can imagine it is like Apex Legends over there.

There are Oliva (new player) servers,  for new and returning players who want fast experience.

All the rest is general content, where I hang out the most.

I hope I covered them all. 

Have fun!

There is a giant annoucement detailing every aspect of seasons on the main page.

Compare seasonal servers to a "Highway" of some sorts.

You can make a seasonal character through the character creation menu, after creating said character you can play on a Seasonal server (or regular server) Seasonal servers offer a easier way of levelling up your character and gear. It's kinda a prep for the normal servers.

Seasonal servers offer a EXP boost and, unless you're on the PVP server, you cannot be killed by other players. (downside being that everyone can grief you without consequences) an dthere is a special server for new players (Novice only)

Something to note is that Seasonal Characters also have acces to special seasonal gear (tuvala) which is easier to enhance and when enhanced on PEN level it is comparible to TET boss gear, take note that these items can only be enhanced with special Tuvala stones which can drop only on Seasonal servers (or as quest rewards).

There's also a shortened questline (only available if you've played through them before) and a season pass (both paid and free variants) which offer rewards as well for completing quests

After the season ends you can graduate and chose different graduation rewards (you can pick one of them only once so dont lose them) including PEN capotia accesories (comparable to a TET accesorie)

All with all my (personal) opinion is that it's definetly worth checking out and doing if you're a new/returning player or a existing player