It depends on your strategy for me I don't wait until 20% for me to take profit, most times, some coins hardly make such gain, but taking profits like 5% or 10% many times could be a good idea, coins normally makes such gain many times before it could go as high as 20%, so I believe in taking profits as soon as you see them and re buy when it dips down again.
Yes right, in my opinion there is nothing wrong when we expect to get big profits, precisely the biggest factor that makes bitcoin prices difficult to rise is because they are too easily panicked so they sell when they get profit 5% or less .