Inline list is what i use most often. It’s just that…a list of items that can be viewed as a list, a compact list, as tiles, as a map, etc. The List Relation is different in that if there are multiple items, it will just show on one line, the number of items. When you click on it, it then opens into a list. If there is only 1 item in a List Relation, then will open directly into the details of that item.
Here is a screenshot of an inline list on top and a list relation below that. Both of them are referring to the same set of date.