Use Google Maps Whenever You Want, On Your Device Of Choice.
Google Maps Go is a free and lightweight version of Google Maps, officially licenced and developed by Google LLC. It is designed to improve over the usability of the standard Google Maps app when running on older phones or networks with poorer reception.
The Same, Yet Different
Google Maps Go provides better performance mostly by tweaking code under the hood. Search results aren't retrieved and loaded as readily as on the map Maps app, for example. This saves network bandwidth and makes Maps Go run better underground or in rural areas compared to Maps proper, for example, but for standard phones, performance has mostly been improved by trimming the interface and unpopular features. These changes aren't exactly comprehensive, so usability isn't affected much, but performance isn't much better on older phones either.
First Steps, Long Road
Overall, Google Maps Go does much better in addressing the problems caused by poor networks than addressing the problems caused by older phones. But Google Maps Go is under development as of this writing, so users of older devices should still keep an eye out for changes, and those using networks in rural areas or countries with poor connectivity will likely benefit from Google Maps Go.