Is $filter query not applicable to instance resource

Hi all,
I got such question in my implementation.

per specification, it has definition for $filter query parameter as:
Include a subset of
the members of a
collection based on
the expression

specified in the
query parameters
for this option
- http://resourcecollection?$filter=SystemType
eq 'Physical'

However, it seems to be make sense too when apply it to some of instance resource like:
perform $select=Voltages&$filter=Voltages/Status/Health eq 'OK' on Chassis/Power resource to retrieve all healthy voltage sensors

May I have your opinion about this limitation?
Thanks

Best Regards
Anson