We are not talking about partisans, but coastal defence. There are many ports in France and Benelux and some people seem to be proposing to guard them with regular infantry, sometimes even more than one division per port O_O. Even if we guard only some of them with multiple divs, that would require sth like... (at least) 30 infantry divisions to cover all ports from Bordeaux to Amsterdam? That's 6 full corps that could be used in Russia. I think that it's a waste, because 90% of the time those troops will NOT be fighting in France, but just standing there and consuming supplies. However, even if we ignore wasted ICdays (which is not that important for Germany in Vanilla from 1941 on), those divs will still "take" their share of MP and LP and one will have to build more infantry (=more used MP and LP) for Russia, anyway. That will either lower the officer ratio or decrease the number of researched techs, none of which is good. If we ran into MP issues, these divs will have to be moved to the East or disbanded, anyway.It's leadership intensive, too. Each of those brigades cost 100 officers...
Beaga is partially right, though. Thanks to collaboration government, partisan activity is really not a big deal in any country that goes GiE or that is continuing resistance because you haven't forced a surrender.
However...
I will say that if the AI made use (or better use) of UR, then this wouldn't be a problem. While many players complain about how gamey UR uprisings are, I will say that the threat of such uprisings would force players to build and use a lot more suppression units. URs are easily rooted out by units with suppression, so if you had to wallpaper Eastern Europe to prevent the enemy from using URs, that would seriously drain IC, manpower, and leadership.
But as far as I can tell, the AI doesn't even use URs, or uses them so infrequently that it makes no difference. Which is too bad; it's a nice mechanic for these kinds of things.
Moreover, I wouldn't be surprised if on higher difficulty levels even 30 infantry divs weren't enough to contain the Allies in the West. In case of a major invasion involving armoured divs a mobile reserve would still be needed... so what's the point of guarding every port with regular infantry, anyway?