well...
You can, but you run a better chance of cracking the PCB or shorting something out by doing that...
It's not a very safe method, but if it works for you...
In a pinch I've also just cutout a piece of corrugated cardboard & sandwiched it between the PCB & the wood I'm mounting it to... It allowed a little protection for the solder points instead of them being jammed into the wood.
But I would definately suggest using some sort of mounting "feet" to suspend the PCB above the mounting surface if you can.
(In other words, do what I say, not what I do...)
