Bitcoin is currently trading higher than it ever has before. If you're holding onto Bitcoin as an investment, how high will you let it get before you sell?
I sell them all the time, then buy them back when they tick lower. There is no point in leaving your bitcoins dormant in a wallet when you can buy and sell in your spare time. I have made about $1000 on top of my $1000 initial investment a few months ago.
I convert them into fiat soon after earning them. Not because I do not have faith in bitcoin but because fiat currency is so much more useful.