Well, it would be nice to have both measurements at the same time (which is how power meters, dataloggers, etc work). If you are getting one reading that doesn't look right, you can see what the other reading is saying. But no, you don't "need" to use them both at the same time.
_paralyzed_, not having multiple meters really isn't an excuse.
You can get them for $5-10 each if you look around (Harborfreight tools). They aren't the best, but for general use, they are perfect. I use my Fluke for precision measurements and the cheapie meters for when "pretty close" is close enough. Although, I "calibrated" my cheapie meters with the Fluke, so they are closer than pretty close.
