I do both as well. And many times I will do a completely pieced back (basically a double sided quilt) with leftovers from the front, supplemented by stash. However, given a choice, I really like the convenience of wide backing. And it really is not more expensive. Most the time I can find it on sale for around $10 Per yard. When I go to Mennonite shops I have picked up wide muslin for $6. But even at full price it is usually more cost effective to buy the wide back.
For example, A Queen size quilt measuring 90 x 100 would require a minimum purchase of 6.75 yards of 44" wide fabric at $7 per yard. This is assuming 3 seams and also assuming the WOF is really 44". I am seeing more and more fabric measuring at 42" or less in width once you cut selvage off. At $7 per yard it will run you $47 (rounding to nearest whole dollar). We are not taking into account your time and effort to cut it down as needed and sew it back together. You will need even more if you are sending to a LAQ who needs extra backing to attach to leaders.
However, you would only have to buy 2.75 yards of wide back at $15 per yard so the cost is $41.25 and you will have enough left over to make binding and add to stash and the added bonus of not having to cut it or seam it. AND the extra length is already there for a LAQ but you might need to buy more for the width to adjust side clamps so even if you upped to 3 yards it still comes to a tiny bit less ($45) than the standard width stuff.