A GPS needs a minimum of four satellites, not three. Maybe you could get by with three if the earth was a perfect sphere and GPS units never left the ground, but that does not happen. More is better so it can calculate positions with different combinations of satellites and average their calculated locations.

I get frustrated with a GPS in a major city center when the tall buildings means that I lose GPS location and can't recover it. But that is the only thing that really bothers me. If my GPS says I am doing 2 mph or 5 mph when I am going slow, I already know I am going slow so I really do not care what it says.

I have a separate bike computer with wheel sensor on most of my bikes too, if I was going slowly up a tall hill and did care about my slow speed, I would rely on the data from that instead of from the GPS.