Dilemma: when to use Fragments vs Activities:

Question

I know that Activities are designed to represent a single screen of my application, while Fragments are designed to be reusable UI layouts with log

Answer 1

In my opinion it's not really relevant. The key factor to consider is

1. how often are you gonna reuse parts of the UI (menus for example),
2. is the app also for tablets?

The main use of fragments is to build multipane activities, which makes it perfect for Tablet/Phone responsive apps.