This question is completely subjective and difficult to answer. I would take a look around the marketplace thread and you will see tons of items created completely in Blueprints … so the options are pretty limitless.
Having said that … Epic doesn’t support C++ items in the Marketplace … yet … so the items in there are subjective to that.
Would I use Blueprints for Data Connectivity? No
Would I use Blueprints for Security and/or Encryption? No
Would I use Blueprints for almost everything else? Yes and then some.
I would say, learn Blueprints, get to know what it can do … if you come across something you can’t do … learn to do it in C++. 8-}