I don't really see the need to SLOP if no one else is around. I also think its silly if my aircraft is SLOPPED and the aircraft behind SLOPS too - this happened a while back and a Jumbo went straight underneath us, setting the RAD ALT off. It seems that only 67% of flights should do it when crowded, otherwise no need.
Given that its not usually THAT busy on random routes and even on the NAT tracks, I find I only use it about 1 or 2 in 10 times, so maybe 10% isn't too bad?