Hello cameron, the principles involved in constant PO2 diving apply for any dive, deco or not. And anyway, all scuba dives are deco dives.
Whether you ascend from a square profile or a multi level, one of the benefits of constant PO2 diving is a smooth increasing % O2 on ascent, no gas switching, no part of the dive where you are breathing a mix that was better for the deco stop you did 20ft below, but not the next one. Another huge benefit is the very small amounts of gas needed at depth. On a square profile/wreck dive, you only need very small amounts of O2 once at depth, to maintain the PO2 as you are rebreathing the gas. And because you are not metabolizing the inert gas in the dil, which is there merely to give you enough volume to expand your lungs and breathe, you will need no additional dil gas once at depth, or for the rest of the dive.
On square dives in particular, you will use very little gas, until you begin your ascent, when you begin to use your more of your O2 supply, but again, you're rebreathing the O2 and only metabolizing a small amount. My CCR instructor routinely gets 10+ hrs out of his 19cuft cylinders doing square profile dives on the Andrea Doria. NE wreck divers were the earliest civilian pioneers of CCR, diving used military gear, like the Mk 15.5. A yo yo profile will cause you to use more gas, but you'd have to do an awful lot of yo yoing to use up the same gas as on OC, you'd probably get bent first.
There is no way to improve on the gas economy of a CCR, unless you come up with human usable gills... -Andy