I just watched a GSTL match between Zenex and OGS, where the Zerg player, with the match on the line, used a Roach-Hydra based army in a ZvT.
Why is this a bad idea? Simply put, Terran almost always uses Tanks against Terran, and Roaches die quickly to tanks, and don't even do well against upgraded marines because Roaches are too big to get a good position against the tightly-packed marines before they lose too many of their number. Worse, Roaches are nice beefy units, but aren't very supply-efficient. Thus, using Roaches in the later stages of the game is a bad idea.