As above, if you are racing and need a few tenths of a second saved on a lap, then it is vital to set everything very accurately including the rocker angles. I such a case it is important to get it right.
For a road car, though, there is a degree of tolerance in rocker angle and the use of this tolerance will never be noticed in road driving, because you are not timing it to fractions of a second and using loads of revs through the gears all the time.
It is easy to spend a fortune ("Hooray" say the parts vendors) on building a fantastically accurate engine and then just using it on the road.
Build a road engine carefully, set things as accurately as possible using spacers and shims as necessary and required, time the cam in accurately and don't use a 'silly' cam. Just use a nice road cam with good induction and exhaust systems, a nicely gas-flowed head and match everything properly.
You don't need to spend a fortune on special high-performance parts, much as certain sellers of such stuff would love you to.
Then go out and take pride in and derive enjoyment from your old classic car which drives so smoothly and well.
However, if you are building a full-on race car in which you want to win races it is a different matter.
