I think an amp is pretty much a must have. My reception is fairly stable, but if it rains or the wind blows, it can start to flake out on me. Amp solved most of the problems.
For many people, yes. However, for some there is the risk of over-amplification, especially if they have a converter box that already has some form of pre-amplifier built into it, or their signal is already at 70-80%. Digital only needs about 50% signal strength to lock on - anything about that is just gravy. If the signal bounces around a lot, an amp will be of limited use, as a fluctuating signal is a sign of multipath interference or of objects like trees between the antenna and the TV station’s transmitter blowing around in the wind.
A good outdoor antenna is still the most important item in any off-air system.