CASA's MOS has lots of specs on required flying tolerances but nought on balance that I can see apart from words like "balance and trim the aeroplane accurately". First of all the instrument has to be accurately mounted in the panel. Secondly, consideration of the behaviour of the ball in dynamic conditions - refer the text in the attached photo.
Worth repeating that first sentence: "Many pilots are under the mistaken impression that coordinated flight and ball-centered flight are always synonymous" with the result that, unless absolutely steady conditions, they fly down final in a state of perpetual uncoordination. The Pitts standard instrument package does not include a slip ball yet it can easily be flown accurately in balance - except normal landings when many of us prefer to sideslip just so that we can see the runway.
As for flying the approach in calm conditions or direct headwind vs a crosswind - the discussion is irrelevant as there is always a crosswind component, its just that sometimes it is NIL.