Cannot understand the significance of the question type rem

I don’t understand the question rem type, and the documentation does not provide clarity. What is the effective difference between the two bellow examples, other than the first one being a question type rem, and the second one being a descriptor type rem?

What is the center of our solar system?:: the sun

what is the center of our solar system?:: the sun

Well the main difference is that the created flashcards look differently depending on what type you use:

This formatting has to do with their concept-descriptor framework. Here’s an example of that framework being used:

Descriptors are flashcards that ask you to “describe” an aspect of a concept. As a visual aid the concept in question is always bolded. Questions however are more or less standalone, which is why only the questions themselves are bolded.

The difference is between the concept and descriptor when you create them on the fly: if the rem starts with a capital letter and you use ::, both forward and backward cards are turned on, if you use ?::, only the forward card gets created.