How did Swiss neutrality affect WW2? What impact did Swiss neutrality have on the Axis powers? the Allies? Did Swiss neutrality have a significant effect on either side?
Neutral Switzerland was an venue for communication between belligerents' intelligence services, and thus was of benefit to all sides.
Additionally, Germany used the Switzerland's famous watch-making industry to circumvent the allied blockade on Beryllium copper, used for springs in watches and machine guns. (The source: a book on history of metallurgy I read ~30 years ago; it claimed that during the WW2 Switzerland imported enough Beryllium for ~100(?) years of its watch-making).
Thus it appears that Swiss neutrality benefited Germany marginally more than the allies.
Swiss army was strong enough to make a German invasion unprofitable, but it had neither will nor ability for an offensive, so its neutrality was somewhat inevitable. In the inconceivable case of Germany invading Switzerland, Heer would have been bogged down in the mountains and MG-42s would have worked worse, so the war would have probably ended earlier.
PS. Even if the Germans overran the Swiss, the occupation forces would have had to be at least comparable to the pre-war border defenses: since no attack from the Swiss can be expected, the border defenses can be very weak; since Swiss (as opposed to, say, Danes or Czechs) would have fought, they would have required a non-trivial occupation force.