Actually you can turn on/off the GPS and very easily.
Download MacroDroid and get the Premium version. The upgrade is an in app thing.
Then set up some macros to trigger when certain apps are invoked. Then set the Action to GPS ON.
Create a 2nd macro to turn the GPS off when you exit those apps.
Personally, I always leave the GPS on High Accuracy and have not found it to have any noticeable impact on battery life. According to Battery Doctor, if you turn off the GPS, you will save about 20 minutes of battery life. Whoopie..... that I can live with.
Back to MacroDroid. Once you start using that app, only your imagination will stop you from thinking of things to do with it. Do yourself a favor, follow Jamie's blog and forum. He is the only developer and he is extremely diligent in answering questions.
He also wrote the app to automatically reapply the Upgrade you bought if you have to Factory Reset your phone and start all over. Now that is something no other app has done in my experience.