[nostrademons]

It's so that if the server update fails, the user isn't mislead into thinking it succeeded. They can then take whatever action needed to correct it, like clicking the arrow again.

It probably doesn't matter much for a site like this, but it's one of those things that's just a good habit to get into. Perform validations first, then actions, then UI updates. And do the actions that are most reversible or most likely to fail first. If you have a POST that updates a DB table and sends an e-mail, update the database first, because there's no way to unsend that e-mail.

It's like comparing constants from the left in C or doing "literal".equals(var) in Java - each individual occurrence is trivial, but taken together, it can save you a lot of grief.

Edit: though looking at the source, it's done through an Image update. I don't think there's any way to trap failure with that implementation, so here, it really doesn't matter.