Does a wooden deck need to be power washed every year?

I have a large wooden deck and I live across the street from a lake, so the deck will get mildewy looking on the edges.

I had it power washed last year, and I oiled it with the clear oil stuff for decks. I paid a guy to power wash it, although I own my own pressure washer, it was actually easier to pay the guy to do it. Doing it myself was a lot of work.

Yesterday, we bought a swing bench that will be placed on the deck. It comes apart and so the bench part will hopefully be taken inside in the winter months, but I think the bracket part will stay outside. I am wondering if it’s bad to power wash a wooden deck every year, or if it’s better for the wood to do it. If so, I will have to get the guy do power wash it before assembling the swing.

Will it rot the wood faster to get it washed every year?