If you have a Garmin watch, you have a choice in your GPS Settings. You can run GPS only or you can select two other settings; GPS + Galileo or GPS + Glonass.
I choose to run with GPS + Galileo. Why? Adding Galileo Satellites or Glonass satellites provides you with a bit more accuracy. One is not necessarily better than the other in our location but both help especially in urban environments or hilly trail courses. The additional setting can burn a bit more battery life but I have the increased accuracy worth it.
I have been using this logic, using GPS+GLONASS for a while. My past few runs have had lousy accuracy, and today’s was outright atrocious. I’m switching to GPS+Galileo just because something has to change. I’m open to any other ideas or superstitions but might contact Garmin.