You're conflating application state with request state. Updating application state based on a request is a perfectly reasonable thing to do, but it necessarily

You're conflating application state with request state. Updating application state based on a request is a perfectly reasonable thing to do, but it necessarily invites the possibility of a memory (or database, file, etc) leak. Either PHP can't update application state at all or it can and necessarily suffers from the same potential to leak memory (I suspect the latter, since an application without side-effects would be worthless).