I have the adjuster cups out. Its perfectly fine for everyday use as theres more than enough weight to stop the springs coming out of place.
I did have an issue when I got new tyres fitted. They lifted both sides of the car at the same time and the springs became unseated, then when they lowered the car back down, the springs didn't sit properly, so the weight of the car was pretty much on the exhaust. I noticed this straight away though, so no damage was done. Best to warn anywhere thats going to do any work that the springs might fall out the rear lol.
Or you could be 100% safe and leave the adjuster cups in