Here is the long and short of it. Why not do it the correct way to begin with. Cutting a pattern or design and placing it on the correct grain will give you the best quality and good workmanship. That is the difference. If you are satisfied with less, ok for you, different strokes lol. Personally I refuse to fuss and fudge and struggle when cutting it on the straight of grain will do the job for me.
I look at quilting as a precise method of a work and the work must be done to the best of my ability and I take great joy in that as I know you all do. I know you want that quilt to look great, after you have spent hours on it.
Take for instance, making a skirt. You would cut on the lenght of grain so the skirt falls nicely down your body. Cut in on the crossgain and will bubble and wave down your body, and look terrible, same difference with quilting. There is a right way and a wrong way.
For years we have been taught (not me, I am a seamstress lol) to cut accross the grain to save fabric. Well that is so much malarky. Not only is this incorrect and your work suffers for it, but here is the test.
Talk one yard of fabric 44 inches wide, (we will assume that the selvages have been cut off) now, cut accross the grain in two inch strips. You will end up with 18 strips (two into 36), 44 inches long for a square inch total of 792.
Now, take that same yard and cut the strips on the straight of grain. You will get (2 into 44), 22 strips by 36 inches long for a total of 792 sq inches.
There is no saving!! so why do it wrong lol.
Now, blocks with all bias seams on the outside will make a nightmare out of your quilt, at least try to have two side on the straight of grain and put those on the outside if possible. Cut borders on the straight of grain, cut accross the grain and you will have extra to ease in, so why do it?
I know the pioneers couldn't care less, they needed blankets and made the quilts out of old clothing or whatever they could find and made them they way they knew how.
We on the other hand, have so much more knowledge, just like everything else, we have learned the correct way as we are not making quilts out of old clothing anymore or out of necessity, (well most of us). this is our hobby, our creations, our gifts for friends and family, our heirlooms etc, etc, etc, lol. We are paying more than 9.00 per yard and we want our quilt to look it, right?
Having said all that, it is just the teacher coming out of me and I can't help it lol. I try not to let it pain me too much, when I hear a teacher teaching some eager students how to quilt the wrong way, I can't save the world lol.