After you have conquered France as the Axis in a west first game, how many units do you leave behind as a garrison?
Depends on the UK/Med situation and how many allies I have (you only need so many garrisons/minor armies in Russia), but not many.
The compulsory three home defence armies can already protect important points like Brest. Before the US there's not that much the UK can do in France, and I find their surprise attack way too important in the Med to be used in some invasion that will ultimately lead nowhere. So, I gradually strat move garrisons west as the US starts to build a presence in England.