I am on Verizon and this is my first unlocked phone. Verizon (and other carriers, I believe) block certain stock apps and install their own apps that you cannot delete. For example, the spam blocking app on Samsung is removed and replaced with Verizon's that requires a monthly fee. There are many examples just like that one.
For me, I travel for work internationally. It is ridiculously expensive to use Verizon internationally for any length of time. I want to be able to get a local prepaid sim card when I am elsewhere and switch them out with no fuss.