A twin needle leaves an ugly zig-zag type stitch on the back. I wouldn't quilt with it.
Depending on the 'size' of your twin needle (that is to say the distance between the two needles) such as 1.6, 2.0, 3.0, 4.0, you can get different effects.
If you have a machine with 'fancy stitches' you can put a different color thread in each needle and get some really pretty effects.
CAUTION!!! You have to reduce the width of the stitch by the width of the needle or you will break the needle and possibly damage the throat plate!!! For example, if your decorative stitch can go as wide as let's say 6.0, and you want to use a needle that is a 2.0 (i.e. bottom of package will read 80/2.0 or something similar) you can use a decorative stitch with a maximum width of 4.0. (That's 6.0 minus 2.0 which equals 4.0.)
I even did a decorative stitch with a different color thread in each needle using just a straight stitch and a zig zag. (15 straight stitches followed by 5 zig zags, followed by 15 straight stiches, followed by 5 zig zags ... you get the idea.)
If I can ever figure out where the @#!# I put my camera, I will post some pictures of decorative twin needle stitching. You can really have a lot of fun!
Peggy