On mechanical RDs, limit screws that are too loose will allow it to travel into the spokes or the chain stay on excess cable pull. However with electronic RDs, its state is known at all times. Assuming it's properly indexed, there's no condition where it can over-shift.
Shimano warns of setting the limits too tight, but what would happen if it's too loose?
In my opinion, you should still keep the limit screws. Sure, you don't need them under standard operating conditions. However, if you somehow hit your derailleur (or something does), the motor and gearbox will disengage due to the shock and then, the limit screw is the only thing stopping your derailleur from going into the wheel. Specifically, it would be the lower limit screw--you could probably remove the upper limit screw without any issue though. You're far less likely to be in a situation where the derailleur is being pushed outboard rather than inboard.
But really, there is absolutely no point in removing either of them. You save what, a gram and a half? If you're really worried, some aluminum screws (or even nylon) would probably accomplish the same job at a fraction of the weight.
I think Shimano only kept the limit screws for historical reasons and because they were afraid of damage caused by bugs or user configuration error. You can remove the limit screws completely and it will still work fine. It’s a bit like the safety pins on their brake hardware and cranksets.
On some Di2 front derailleurs (e.g. FD-R8150) there are no limit screws at all.
I work for a big company which makes electronic hardware. We have a ton of superfluous features which are only there for historical reasons or for some more or less justified concerns (“But what if a bug in X causes trigger Y to fail, let’s keep this firmware bit we had for the last 5 project generations so it can be triggered manually!”). Getting everyone to agree to remove a feature is always a huge struggle. It’s really become a pet peeve of mine.
