I'd definitely sell some when it looks like the price might have reached the cycle's peak. I'll be aiming to sell around half of my stash (depending on where the price will be) to help me finance some purchases to improve my own and my family's life. For the remaining part, I'll probably sell also around half of that (so ~25%) and try to buy back when bull run ends. But, as historically I wasn't doing that great in predicting market trends, I'd like to just hold the remaining 25% (i.e. in case I make a bad call and bull run keeps going). I don't intend to ever sell 100% of my bitcoins and would like to pass at least some to my children at some point.
Well, selling is the most intelligent thing to do when the market reaches the peak of the cycle. then wait for some time and reinvest if we feel that Bitcoin had already reached the bottom. If we are wrong in our assumption then we can always cost average until we are satisfied on the average cost of our investment. This way we can easily grow our Bitcoin portfolio over the course of time. Just repeat the said strategy every cycle and we will find ourselves holding way more Bitcoins that our initial investment.
That said, I am also selling part of my holdings if I feel that Bitcoin had reached its peak and rebuy when the price become cheaper.