My greatest issue with jack stands is lateral movement of the floor jack. Always be aware that the floor jack is GOING to roll and have it positioned appropriately.
when I was younger, I would work with just the floor jack, never had a problem. then as I got older, I got more paranoid. started using cinder blocks with no problems.
Got more paranoid, started adding wood strips to insulate the blocks from busting.
Paranoia increased yet more, and I switched to cheapie jack stands.
More PARANOIA and I now use heavier jack stands. And I am VERY cautious with the floor jack any higher than 50%.
I think in a few years the paranoia will induce me to replace the Sears ATV jack with a 300$ 10 ton low profile unit.