[TECH]:: Gains from adding GLONASS satellite data to GPS based navigation system.

[RussellMc]

In geographically open situations, GPS based navigation system accuracy is
not generally improved by adding GLONASS capability.

In situations where sky-view is reduced by terrain or foliage or when
passing under obstacles (bridges etc) adding GLONASS capability usefully
improves system accuracy and reacquisition time in many cases.

https://www.oxts.com/technical-notes/what-does-glonass-add-2/

2014 article but appears still relevant.
GLONASS coverage is now almost worldwide most of the time.
Scattered areas of temporary lower availability occur towards the equator.



Russell