Icons and Invitations
Aside from the rare in-person session I've been a VTT GM for over a decade now. So naturally I've built up a library of maps, tokens, etc. to throw up in Roll20 (or more rarely Foundry) for my games. Around this time last year I considered consciously moving towards a unified artstyle for all the tokens I use, but decided against it because I found a certain charm in the range of art and styles that ended up in my games. Thinking about this again recently, I've arrived at a reason for why I felt this: it works against me as the GM unilaterally imposing my vision of the campaign.
The thinking goes that if I, as the GM, set up the game such that everything looks similar it communicates to the players that this is how the world of the game is, and therefore they should attempt to fit within those perceived vibes. Conversely if the way I present the world to the players is not uniform it tells them that I'm not worried about keeping a firm grip on what is/isn't allowed at the table so they're more free to contribute their own ideas without having to worry about whether they conform to my vision as the GM. Presenting a disjointed artsyle invites the players to contribute more of their own personality to the game, is the idea.
That's the theory, anyway. I don't have the means or inclination to collect data to prove it. I also am not and cannot say that this is the way for every campaign or table. All I can do is reflect on how I've been running my games and what that implies.