> And why would anyone need to be able to verify that?

Because, in the bank example, after a bank transaction happens, the artist may not like a particular supporter because, for example, the supporter may be a white cis male who doesn't like the left bullies, so the artist may lie that the transaction happened at all, saying that he/she didn't receive any money from the supporter. In this case, and other such cases, there must be an independent log of events that actually happened, despite what people may say.