what is its purpose? is it really needed for a carburated car?

Its needed. It lets the fuel expand and contract with temperature. It connects to the charcol canister so you don't smell fumes.

Also required by DMV & CARB for emissions control, which is still required to have all original eqpt. for smog controls for that MY - even when in the exempt years.

IMHO, I'd keep it intact with the return air hose into the aircleaner or stack(s) on your carb so it "looks" legal & essentially works the same as when connected to the EFI's aircleaner box, & won't put fuel smells in the cockpit. Otherwise, disconnect the air supply line from the fan shroud so it won't push the fumes through the filter cannister.

Technically any conversions or adaptation (i.e.: carb conversion), then DMV can for you to put it all back to OE (assuming they know what that was), then have you smog checked to the old MY specs before it's legal to register again. That hasn't kicked in for older vehicle random inspections & roadside "sniffers" yet, but is supposed to soon.