Can you tell if the market will go sideways? that situation could destroy an account under trend following strategy. Don't get me wrong, I try always to stick to the trend, the problem you'll never know when the trend is really changing, so there's a toll to pay when you're positioning in an allegedly new trend coming, no easy at all.
Nobody can do that. When you reach your profit target get out. Or stay in, if the trend is still good. How come traders are more scared of trends than any other chart formation? Probably because plenty of people have bought into a trend of rising prices (like dumb-ass buy-and-hold investors have done through history) and then they go to sleep on the job. That's not something I'd recommend.