Yes a GPS is unnecessary for the average rider but if you're in new territory, if you're training, if you're doing a 'permanent' randonnee course, if you want to look later on a map and see just where the hell you went wrong then a GPS is handy. Saves trying to find someone in the middle of the night to sign your brevet card and verify your Audax ride.

I have two Bryton GPS units, their 60 and 30. The former has maps but 12 hours life, the latter is more basic but 30 hours. Bryton claims higher battery life but I don't have that luck. Nor did I when I contacted Bryton years back after Garmin did a software update to allow their higher end models to recharge on the go without rebooting, Bryton hadn't considered it and I think still haven't modified their models. If I try to recharge while recording it switches off the recording to reboot. Technically the 60 can hold more ride data than the 30 but will never stay powered long enough, unless my bike has jetpacks I'll never exceed distance over hours running. So I'm working on a solution too.