It might not. Depends on what you want a PM for in the first place, and it also depends how you pedal. If you're doing 50/50 at all times, then measuring one leg and assuming the other is the same works really well. If you do 60/40 at lower intensities and approach 50/50 when you're going all out, then you'll be off by 20 % sometimes.

I went with bilateral measurement because the left-only pedal was $700 at the time, and that's just way too much money to spend and still not know my power output.

Crank or something would be even better, but I wanted it in the pedals for portability reasons.