Sockets are not important but the CPU compatibility across sockets if you use your CPU for a long time.
Outside FM1,looking at AMD CPUs and the platforms they could be used in for the last few years:
1.)AM2 Phenom II would work in AM2 and AM2+
3.)AM3 Phenom II would work in AM2,AM2+,AM3 and AM3+
4.)FM2 CPUs would work in FM2 and FM2+
The problem with Intel is highlighted by my own experiences - I am on socket 1150 still and when my motherboard died,a few years ago,Haswell had just been released. I have a mini-ITX system,and all the choice that was left under £120 was a pair of B75 ones and loads of rubbish H61 ones. I ended up with a motherboard worse than the one I original had in many metrics.
If it had been a year later,I would probably either have had to get a totally rubbish H61(if I was lucky) motherboard or replace everything.