Is thermal paste a must on all builds? When would you not need it?
Thermal paste is usually for the CPU fan. if the fan already has thermal paste on it then you dont need it
I don't think there are any circumstances where thermal paste wouldn't be preferable. I would also not run a build without thermal paste, as I think it's a must.
Why are you asking?
If you use the stock AMD/Intel heatsink, it comes with its own paste. If you buy an aftermarket heat sink, it probably will not come with paste and you must buy your own.
You cannot put metal on metal if thats what you're asking.