power equation of the signal(contineous or descrete)

as we know that power equation of the signal is given as
P(t)=integral(t1 to t2) XSquare(t)
also
P(t)=integral(t1 to t2) Xmodulus(t)
to make the negative sign of signal positive.
My question is why we use equation no. 1 instead of of no.2 more frequently.? Is the answer is more reliable or what.?

plz help me this.
thanks