How useful would it be for law enforcement? It's not even GPS level data, just a rough location fix based on nearby cell towers. That might show you miles from your actual location. The data is likely kept as a cache. Android phones do it also, they only keep the most recent data.
The long history of data kept on the Apple phones maybe just be a programming error or oversight.
This is a tempest in a teapot. It's great for headline grabbing and morons like Ed Markey and Al Franken to bluster about.
It isn't useful for law enforcement... it is useful for quick zeroing in for the GPS so that users only have to wait seconds instead of having to wait minutes for the real GPS to find their locations from the satellite GPS signals. Apple uses Cell Tower assisted GPS geolocation based on this database... and it is fast because most people stay within a specific area and use cell towers within that area. Apple's Core Location system stores the specific location information for those towers in this database and doesn't have to ping them every time to assist the GPS system, thereby speeding up the display of where the iPad or iPhone is located on the screen... making it much more usable for the owner. Those who have turned off their database caching are finding their mapping, routing, and other apps that use these abilities are crippled, drastically. That is the stupidity of this panic.