My dad has it, and I need to get myself checked out for it as I think its 50/50 I will have it.
As far as he understood it, and how he explained it to me, it’s just an issue with the breaking down of bilorubin which can lead to becoming jaudiced and getting the yellow eyes thing. Only an issue in so far as he was recently admitted to hospital for something unrelated and his eyes were going yellow as a result of the stress the unrelated thing created, had he not know he had Gilberts then the assumption would have been made that his liver was failing.
So useful to know if you have it, but no effect on your day-to-day life.