I'm in the process of rebuilding a 600 cfm edelbrock (mech. secondaries and manual choke) and noticed there are a second set of butter flys in the secondaire barrels, they are only connected to a set of waits.. what are the purpose of these and would there be any benefits or harm to take these out?

Its going on a stock 305, only mod that will be made while the carb is on is headers.

 

You don't have what is commonly called "mechanical secondaries". You have mechanical secondary throttle blades whose ill effects are countered by that second set of butterflys connected to that weight. Similar designs include the Carter AFB, and in somewhat different form, the quadrajet. Another non-mechanical secondary carb form is called vacuum secondaries (where secondary throttle blade opening is accomplished by a vacuum diaphram, opened by flow through the primaries).

A true "mechanical secondaries" carb is a Holley or Barry Grant Demon double-pumper. The ill effects are countered on those carbs by a 2nd accelerator pump tied to the movement of the secondary throttle blades.

Removal of the 2nd set of butterflys in your current carb would have the effect of major bog whenever the secondaries are opened. Don't remove them - they're there for a reason.