Ddgonzal is, as usual, 100% correct.

If you draw vacuum for the distributer direct from the manifold, you get full vacuum advance at idle, assuming that it actually develops vacuum at idle. [I dont know your cam specs.] This is BAD

If this is a road engine, then you will want to have the vacuum advance wotking in an attempt to increase operational efficiencies at part throttle, like in cruise mode. The ONLY way to get the correct vacuum signal is to use the ported vacuum fitting on the / a carb.[It does have one doesn't it?]

This port is just upstream of the throttle plate, so that when the plate is at idle, this port sees NO vacuum at all. As the throttle is opened, as in full throttle, there isn't enough vacuum to suck fizzy drink up a straw, so you get mechanical advance only.
Once you are up to cruise speed, the throttle is reduced & this port can see some suction. This results in more acvance & increased eficiencies. Read this as, "improved fuel consumption figures" which is what you want when just cruisin'
Stab the pedal, throtle opens, vacuum vanishes & ignition timing reverts to centrifugal control only, It works a treat, but manifold vacuum at idle messes with your traffic driveability & thats a pain.
Chris