1) Society. You can ask yourself a similar question about the things you wear, and in the game: social environment, it is important for people to assert themselves in the eyes of others. Someone will say or think that since this player is stocked with things (especially when expensive), it means that he is dragging, it means that he has a good impression and a positive attitude towards the game, but not always.
2) things can serve as an increase in motivation to play with this particular weapon / character. It gets boring to play the same even if you play well, changing the look will help prolong the game.
3) Convenient. Yes, it happens so that it is convenient for the eye, namely, changing the model, accompanied by sound, color, etc.
4) Trade in things
When you play some kind of toy for a long time, for years, it really influences :) For many gamers, the appearance of the character is really important, some identify in some way with their level 110 elf, and if you don't feel sorry for yourself money for jeans, why should an elf feel sorry for a new outfit? I play WoW, bought mounts (mounts) for real money a couple of times, when they asked what to give me for my birthday - among other things, I suggest buying me a mount from the Blizzard store, to please the elf.