Not unless you just use the phone for calls, texts and web surfing. It's severely restrictive to the processing power of the CPU and GPU and also stops GPS working. What you can do is use adaptive battery mode for apps. The phone learns your usage patterns and will suspend apps you are not using to save power
Unless you are low on battery or not near a charger for a length of time, you shouldn't need it. You've got a powerful phone, why not use it. Otherwise pointless getting a phone with the features and processing system if you curtail it. Personally if the phone has the abilities and features, then I'm going to want it all available and I do set everything up to max normally and still get a day out of the battery normally
I remember on my previous Samsung device I had my power saving mode turned on automatically whenever I battery has a lower percentage. It usually starts to turn on when it goes below 40% i think. I'm not sure.