Yes, having a set of tanks per mix is very handy. I have three sets of double 80s with 32, 21/35, and 18/45. It makes it handy to always be ready for what the weekend brings. Eventually you'll get blown out of a tech dive and want to do rec instead or have 32% in your tanks have an open spot for a Hydro Atlantic dive.

If you want to be cheap and laden with gear. You can leave the 21/35 in your doubles all the time and keep an AL80 stage of 32% ready to go. For a rec dive, that means bringing 4 tanks on the boat which won't make you popular, but it gets the job done cost effectively. You could also dive the 1500 of 21/35 on a 100f wreck, leave the "rock bottom of 500-700 psi in there and dive a stage AL80 of 32% on the 2nd dive.

That being said, don't ever, ever, bleed or waste helium! Double 80's 1500 psi of 21/35 topped with 40% at Fill Express gives you "Matthew Mix" of 30/15 which is a great recreation mix. It makes a 100ft wreck seem like a 50ft reef dive. I often dive this for fish counting deeper than 80ft.

Just DON'T top 21/35 with 32% as you will get 27% which is just a mess. I have done that more times than I care to admit out of habit of always and only going for the 32% knob at Fill Express http://www.fillexpress.com. :)

Either way 27% - 32% I dive a Nitrox 32% profile without issue.