But it's not necessarily the bolt's strenght (grade 8.8, 12,9 etc).
Torquing a bolt down prevents the bolt from coming slightly loose. That might cause the bolt to wobble in the bolthole, and that can crack the bolt, or the mounting piece.
A bolt is only strong when it's firm&stationary.
I had that with my rear diff bolt, where I used a new type of polyurethane bushing.
Turned out that the core of the bushing was too weak, which ment it got crushed a bit and the bolt got minute play (so lack of torque, it lost it torqued down spec). Ample time later... the bolt cracked.
Lack of torque can cause the bolt to flex back&forth, giving metal fatique.
So too much torque and the aluminium housing (the threaded hole) can crack (or the bolt can break/strip), and too little torque can cause the bolt to come loose (come out) or flex and break.
So the correct amount of torque you need is somewhere inbetween
