[user104658]

This came in after my time HOWEVER I reckon I know the answer anyway, and it'll be player safeguarding/observation. It's designed to stop people going "over the top" with autoplays e.g. you could in theory have 10 different sites on 10 different games all autospinning at the same time. It's also all automated whereas IN THEORY in a shop there'll be a spotty 21 year old supposedly making sure you're "gambling responsibly" by monitoring your activity from behind the counter. Supposedly.

Anyway. In short, it's to place a limit on your £ losses over time, so that you can't (easily) spin on multiple games at once in different browser windows.

Official rules in shop say you can't play more than one machine at a time also, staff should stop you from doing so. In reality, most bookies will turn a blind eye to a big-staking regular playing two machines at once (so long as no one else is waiting to play). I did once have a chap trying to play all 4 machines at once and - as funny as that was to watch, as one of the machines was on the other side of the shop (and it was a large shop) - I did have to knock that on the head.