It’s not necessarily related to wealth (except that you need some savings), but when ING Direct was a thing my wife and I had an account for every savings goal and used it as our “envelope” system. There was no cost per account and you could open one in seconds, so we had a bunch of low value (dozens of dollars! Dozens!) accounts for saving for our next phone or vacation. That could have been done with a spreadsheet, but it was less work to just make separate accounts.