Most of my life I've done seat-of-your pants quilts. If you require exact sizes and piecing, then consistant seams are needed. If your quilts evolve as you go along, it is not so much. I really would not go skinnier on seams if the finished product was going to be used and washed in a machine, just because fixing tear-outs is a big pain in the butt.
I find wider seams easier to work with on curves. If I have to clip a little to ease them in, I am more comfortable having extra.
Also, a lot depends on the style you are working in. Some patterns demand precision and uniformity, some don't.