On the API/database level, a way is just an ordered collection of nodes with associated tags.
A relation of waypoint nodes is… also an ordered collection of nodes with associated tags.
The nodes that are part of the collection can have their individual tags in both cases.
There is little difference just purely on the data representation level itself. The main difference is how they are usually represented to mappers in editors and end users on a rendered map. That is purely convention based on how they are commonly used and nothing prevents renderers from displaying a ‘pathless’ way that is just a collection of waypoint nodes in the same way they would if it were a relation.
There are some differences between using ways or relations for that purpose though that should be considered:
- Ways are much easier and more convenient to edit than relations
- Relations can have additional information about each member via their roles
- Relations can have other element types as members while ways are only limited to nodes
(However, I think this discussion would be more suitable for a different dedicated thread.)