NO SEWING! (big deal if, like me, you have no machine) And they're less permanent so more versatility in your setup.
A knot is going to use more strap length then a sewn loop. For a 2in loop you are probably only going to need about 3in of extra strap to fold over and sew to make the loop. With a knot you are going to eat up alot more strap length to get a loop the same size. More weight, more material to buy...
A 1in polyester strap has a break strength of 3800 lbs. (figure from strapworks
) so even with knots you have alot of wiggle room for derating their strength. Hang safely.