After Feb 17, they'll improve you OTA reception tremendously, because without one, you'll get no OTA TV signals.
ATSC is digital. Digital and analog signals work differently. With analog, a strong signal gave you a good picture, but as the signal got weaker, the quality of the picture degraded until finally, you just see snow.
With digital, instead of picture quality being a gentle slope, it's more like a cliff. If, you need a 40% quality signal to get a picture, you'll get the same quality picture anywhere between 100% and say, 42%. Between 42-40%, you're on the edge of the cliff, and there will be macro-blocking and intermittent signal loss. Below 40%, and you've got nothing.
So, if you live where digital signal is in the 40s-70s, you'll probably have a lot better picture than you did with analog. If you're in the 80's or above, you probably had a very good analog signal, so there might not be much difference (unless you're also comparing HD vs SD). If your digital signal is below 40% (on my made-up scale), then you might have been better with analog, as you might have been able to make out something through the snow, whereas with digital, you get nothing. But it's a moot point: after Feb 17, digital is all there will be, with the exception of some repeaters and a few low-powered stations, who have a bit more time before conversion is required.