Slight difference between you doing service for someone else and a homeowner plugging away at the keypad not fully knowing what the account number, format and receiver number really does. Also say a tech has a chip on his shoulder because he's taking over a system from a company he used to work for.
I've seen the results of both over the years, also with many companies only certain panels can go to certain phone numbers, for example with Westingouse we had all WS5010's on 2 phone numbers, these panels used 10-digit account numbers using SIA format, putting a standard PC5010 on that line sending
4-digit SIA gums up the works and MIGHT get someone else dispatched on. Same with Honeywell's current V15P/20P using 10-digit Contact ID which the company I work for currently uses..