While I rarely use the free WiFi on board, on account of the limit being hilariously low, it has come in handy a few times when I've had to quickly send an email on my laptop and I was running low on battery on my phone so didn't want to tether.
Having said that, I've had unlimited data on my phone for over a decade now, so I can't really say I'd miss it!
RE: WiFi on Arriva buses