It can be used to identify a location, but not an individual.
I assume it could be easily challenged in court (network was compromised, “i give out my WiFi to anyone who visits my home”) without other supporting evidence.
Not in Germany, where you are responsible for the Wifi access, see hundreds of copyrights fines each year...
Anyway, it puts the persons living in that location on the radar of the police, and other evidence can be collected (For example by getting a warrant and taking all electronics out of the "location").
Apparently in Germany you can do public wifi now, but you have to register as a telecommunications provider, and comply with all law enforcement requests to wiretap your wifi.
I assume it could be easily challenged in court (network was compromised, “i give out my WiFi to anyone who visits my home”) without other supporting evidence.