I do a lot of floating point math at work and constantly run into problems either from someone else's misunderstanding, my own misunderstanding, or we just moved to a new microarchitecture and CPU dispatch hits a little different manifesting itself as rounding error to write off (public safety industry).
If you expect bit-for-bit reproducible results, then yea, you'd have to know about the nitty-gritty details. The values should usually still correspond to the same thing in common real world precision though.
