Do you refresh your page content often?

I've been reading about refreshing page content often but I don't get it.

We sell services. Our list of services, features, pricing has not changed for 3+ years now. Should I make changes to the content, even though I do not need it to, just to keep G happy and help improve &
maintain my SERPs.

What is a general thumb rule you follow?

Note: I'm heavily dependent on Google for my leads & it works best for us.