I'm good with drafting a CB and an OL every year, but with only 3 or less roster spots available at QB it seems like you'd either be chewing through them every year, or replacing them before they develop.
Drafting one every year suggests that they'll show in training camp, and I don't know if a 5-7 round QB would get enough quality snaps to draw a conclusion.
Now keeping one on your practice squad should be a no brainer.