For me, it depends on the card. If it is a high dollar card that is notoriously off centered (i.e. the majority of the cards are off centered like the 52 Bowman Mays) then I have no problem adding an off centered version of that card to my set...I will not pay a premium for a rare centered copy.
However, if a higher dollar card can be found fairly easily with decent centering, I will NOT try and save money by finding an off centered version...I'll buy a reasonably centered card for market price.
And for common cards to fill my set...centering is not an issue. While I wouldn't want an entire set of off centered cards, i don't mind my commons being a mix of centered and off centered...and sometimes I will intentionally pick up a cheaper common that is very off centered to allow me to check it off the list at a lower price.
The 1952 Bowman set is great example. I'm fine with an off centered Mays (because the majority of them are off centered....but I held off on buying a Mantle until I found one with decent centering (not 50/50, but not bad)...here are my copies of both of those cards from my set...and I'm very happy with each one):
Mays.JPG
Mantle.JPG