I've noticed in a few different games that Helvetia seems to play a very key role in the power politics of western Europe. As Austria, grabbing (or allying with) Helvetia means that France and Spain have to hobble through the province to get to you (Tyrol does the same thing, but is less useful if you have expanded into N Italy). Watching all their useless cavalry fall down mountain ravines as my artillery-heavy defending army beats back 3x their number is pretty fun. As England, allying with Helvetia means that whenever France or Spain declare war on you, the Swiss armies don't do much, but the enemy AI makes a beeline straight for the province and sticks about 90K troops there to besiege it while you burn Paris or the northern coast of Spain to the ground. Again, they lug a bunch of cavalry with them, so attrition usually takes its toll, giving me time to force a peace elsewhere.
So, to sum up, make nice to the Swiss.
So, to sum up, make nice to the Swiss.