If your movement are restricted to few locations and has ample access to charging than you may not have much worries about charging smartphone. But think of a situation where you do not have that luxury and you are keen to play games intensively, than having a power bank is almost must for you.
There is one thing a app need to always to keep up with i.e. adding newer and newer features to keep it exciting for end users. Every app there in the market you can analyze would show this in their history.