I just finished my first flannel rag quilt, using 1 inch seams. It is bulky looking. Good for a gift for a male. If using cotton quilt fabrics, I will use a half inch seam for a lighter look, not to mention a larger size quilt.

I've read that 1/2" is a good seam because anything larger will look lumpy once clipped.

Whatever the size of the seam allowance, I poke just beyond the seam with my seam ripper and then just push to the outside. This makes the cuts for the rag quilt easily without any chance of cutting into the seam. Just poke and push.

I use 1/2 inch for rag cutting. Especially if the block is less than 6", otherwise you lose the look of it.

I find the best way to know what you like it to make a small 10 by 10 inch sample piece with multiple seam allowances. After you put it through the wash and dry cycle a few times you will know which one you like best.

My first rag quilt I used 1/2 and it was great.

Depending on how much nap/rag I want I use 1/2 to 3/4. I would be concerned with using anything smaller than 1/2, I would spend more time repairing seams after clipping.