I personally do not like 50/3 thread for piecing and quilting. 50/3 cotton is a standard size sewing thread. For accurate piecing, Aurifil 50/2 works better for me (Prescencia 60/3 would be another good one). The latter are very fine threads, which means I can load more thread on the bobbin and have fewer bobbin changes. They are also very lint-free threads, which means I can go longer between cleanings of the sewing machine. For quilting, I prefer polyester thread (Glide) over cotton because it does not stiffen the quilt (I like to quilt heavily) and it adds a little sparkle.
I rarely buy 50/3 cotton thread of any kind anymore. I just think there are better threads out there for piecing and quilting.