Having Premium gives the following things...
Three Hundred(300) more Storage spaces.
Access to your own personal Shop to put items up for sale to other players.
Access to larger My Rooms that have 150 item space limit, the default room has 5 space limit.
Easier access to various blocks when they are busy, by way of the Premium space on each block.
The ability to trade in 10★ Units, 10★ Weapons, and 11★ Weapons, for a Pass of that same type. Passes can be used without Premium, but can only be obtained with Premium.
The ability to trade items with other players. I am not certain, but I believe they also need Premium in some cases.
Extra FUN from Good Job messages and any multiplayer interaction that gave FUN.
40 slots for Client Orders instead of the usual 20.
Two log-in stamps a day.
Three more crafting slots to work with.
Access to Team Storage (your team must have purchased it. You don't need premium to purchase, but any member that wishes to use it MUST have it to withdraw/deposit)
Additional FUN from using non-NPC friend partners.
Access to premium drinks that give a 15%(?) rare drop boost that has 100% chance of occuring, as well as give the maximum boost for that type of drink.
You can save up to 40 symbol arts.
If you use an AC makeover pass, you have a full hour to keep making changes even after leaving the salon.
All free to play games have these types of perks but only few games can still be played and enjoyed without them. Tera Online has great sub perks but isn't needed either to enjoy the game. Things just take a little longer to achieve is all.
The whole Xbox GamePass thing needs to stop being brought up. It's a perk of the GamePass and not a Perk of PSO2. People get the GamePass on Xbox/PC because of the games 1st. Getting them for just some throw-in items of next to no value is truly wasting money then.