Some phones doesn't have slot for microSD cards - even some companies don't implement it to their flagship devices. If you are using many apps after some time may appear a problem with a small amount of internal storage. Google in the latest update of Google Play Store added new interesting feature which will help will help with cleaning our phones.
If you don't have a lot of available storage on your phone, after opening of Google Play Store in “Updates” section you will find a window which will inform you that "You're running low on storage". Then you may use "Free up space option" - after taping it there will open a screen which will show you which apps which are rarely used, and then you will have option to delete them. This option will surely help people with some older phones.