You have no choice, they have your address and will send you a bill for a random obligatory insurance company if you do not choose your own.

So if you stick your head in the sand, they will bill you around 260chf per month from the day of your registed arrival. It is wise to find one yourself as the kanton won't likely pick the cheapest insurance.

You will also need travel insurance on top of this if you travel a lot. Sorry, the Swiss make sure you cannot avoid their system..