How many dependencies must I set up?

I've read quite a few posts and blogs on groups and dependencies, and I still have one question regarding basic design.

Lets say I have a simple topology such as:

NPM--> RouterA--> SwitchA--> SwitchB--> SwitchC--> and so on and so on...

Is it enough for me to define Router A or a WAN interface on Router A as the parent of a group containing the three switches (and beyond), or must I configure multiple nested P-C relationships in order to be able to conduct root cause analysis correctly?

In other words, do I really need to create:

NPM--> RouterA (P1)-->SwitchA (C1)

SwitchA (P2)--> SwitchB (C2)

SwitchB (P3)--> SwitchC (C3)