I like to measure my returns on a quarterly and year-to-date basis. If I made money last year on an unrealized position, it's no comfort if I lost money on the position this year.
One of the problems with long-term positions is that you can lie to yourself about how well you're doing in all sorts of different ways. I do review long-term positions from time to time and my stops are a lot looser than in my trading account.
But I strongly avoid letting positions get out of hand on the downside. Cut your losses short and let your winners run is an old adage that I try to follow.