Why should I care if the fabric is straight of grain? I've been reading the 'torn vs cut' thread for the pros and cons of that and it all seems to come back to getting the fabric straight on the grain but no one has explained why it needs to be straight when I'm going to cut it a million ways and sew it five ways from Sunday.

I have never worried about it, but I am interested to hear everyone's opinion.

I was told that it didn't matter as long as I had my seams stright and was careful when I was pressing the fabric so I didn't streatch it out of shape. Also, I was told to alternate the directions I sewed when sewing strips so they would not bow. I sure someone with more quilting experience can give you better advise.

if it is not straight (on-grain) it is bias...and very stretchy...
your edges will lie flat if your pieces are cut straight. if you cut off grain your pieces easily stretch out of shape. also if you fabric is not folded on the straight grain and you cut a strip you get those little V's in your strip at the fold....patterns (including clothing and other sewing) often have a line/arrow showing which direction the pattern piece should be placed on the fabric ensuring it is situated correctly (on-grain) things do not (hang/drape) correctly if cut incorrectly
if you want your borders straight, if you want your quilt to be square, if you want it to drape evenly...it is important to cut correctly--on grain

who ever told you that...has not had much experience sewing. i was taught the importance of paying attention to grain when i was 8 in 4-H...that has not changed, and it does not matter if it's quilts or clothing...grain line is important if you want your finished project to hang/drape straight/square.

??? So to make sure it's straight on grain ... before cutting strips you would tear off a bit and line up the two sides and re-fold the yardage? Is that right?

It's less of an issue when you are cutting the fabric into small pieces.

It is a really big issue if it's backing fabric. Your quilt top will be rectangular... and you don't want to pair that with a piece of backing fabric that is a parallelogram or diamond-shaped.

I don't like tearing fabric. It leaves microscopic damage up to 2 inches from the edge of the tear. This is especially true when tearing cross-grain (across the width of the fabric), as would be done in a fabric shop. Tearing along the straight-grain does less damage to the fabric.

For quilting purposes, it is not critical to always be exactly on-grain to the thread. It's more important to be close to on-grain for piecing. For example, you want the edges of your quilt top to be on-grain so they don't stretch out of shape from handling during sandwiching, quilting and binding. Bias edges must be handled very carefully to avoid distortions. For cutting out strips and pieces, it's enough to be close to on-grain; it doesn't have to be perfect!

With garments, grain is extremely important in order for fabrics to drape properly over the body. Quilt tops that are made out of many small pieces of fabric are going to have grain lines going every which way. Keeping strips and pieces cut close to grainlines helps ensure piecing accuracy so all pieces fit together in the end.

Edit: I would add that most quilters do not tear fabric to determine straight-of-grain. It's enough to "eyeball" it by lining up selvedges. Where we need to be very precise is with the cutting angles. For example, once a fabric is folded, a cut needs to be exactly 90 degrees from the fold (not the selvedges!) in order to have a straight cut when the fabric is unfolded. The cause of the dreaded "V" cut in strips has nothing to do with grainline, but everything to do with whether the ruler was positioned exactly 90 degrees from the fold line.

For patchwork, as long as you are close to grain, piecing will usually go well enough. For setting pieces, sashing and borders, grain is much more important. For best results, borders should be cut lengthwise for quilts. Fabric that is cut too far off of grain becomes much more stretchy, and can result in quilts that don't lay flat.

Shouldn't of opened this one, my head is spinning! hehehe