When I was learning C++, it was conveyed that structs were more for combining like data that didn't necessarily require a class because it had a bit less overhead. An example would be a lot of variables that are related, but have no methods (such as a creating a node data structure for making an implementation of a linked list or tree).
Though the above was related to C++, that's generally when I use structs for C# as well.
Though the above was related to C++, that's generally when I use structs for C# as well.