When you use Google Maps or any other service that needs your location, your Android phone doesn't only rely on a GPS signal to quickly find your position. It also uses other clues, such as which Wi-Fi networks or which cell towers are closest to you, which the company maps via crowdsourcing and Street View cars. You can set your phone to GPS-only, but what if you want to hinder Google from collecting data on your Wi-Fi network? There's a solution for that: Just add "_nomap" to the end of your SSID.
This trick is already pretty old and has been around since 2011, when Google was forced to create an opt-out solution after data collection concerns in the EU, following the introduction of Street View in Germany. Google also notes that the "_nomap" opt-out is only valid for its own location service, so other companies could continue collecting your Wi-Fi network's position despite the suffix. For example, Microsoft requires you to include "_optout" somewhere in your SSID, so you'd need to create an ID such as "1234_optout_nomap" to reject both services.
Why would you even want to opt out, you wonder? If you're adamant about protecting your privacy, this will prevent your Wi-Fi network and its location from being saved to Google and Microsoft servers, helping you leave behind fewer traces of your location. Note that Google says it doesn't save personally identifiable information in these databanks, so the opt-out could really just be of limited benefit — it's still better than nothing, though. It's also useful for mobile hotspots as these frequently change positions, which could potentially confuse other Wi-Fi devices polling for location.