You have the vacuum actuated piston inside that has vacuum on one side and that that hole is the vent on the other side.
Whomever says plug it doesn't know what they are doing.
Actually I do know, at least enough to ditch the junk Eddy and get a Holley. Edelbrock added that "cooling" port rather than make the choke cap out of bakelite as the early caps were made of. See above pic of early Eddy choke housing- no hole.
