Yes, if the initial (static/base) timing is too far advanced, it will have very good low speed acceleration but won't rev over say 4000 rpm under a load. This is why a custom curve will help, get it advancing fast, but not too fast, and the engine will return additional HP at all RPMs.

Free additional HP.

Note that simply changing the base setting from 7 to say 14 degrees can have a detrimental effect at high speeds -- starting with pinging/knocking and ending with detonation (pre-ignition damage). It depends on various factors like grade of fuel used, and how much advance your engine can handle. Stock A12s are factory set to maximum 32 degrees total advance, which is a very safe setting. Setting it to 14 initial results in 35-39 degrees total (depending on your distributor's manufacturing tolerance) which is way to much. A14 might handle 36 well, but not the A12.

This comes into effect mostly at full throttle. At part-throttle, more advance can be handled by the engine. That is the purpose of vacuum advance, to advance the spark at part-throttle. And explains why racers don't use vacuum advance, as they don't compete at part-throttle.