So, since version 5.1 the inventory service became a separate / stand alone component of the vSphere suite. You can install it on the vCenter itself or on a dedicated server.
My first thought of it was that it is used as in memory caching service for the web client, so it can serve read request and decrease load on the vCenter service, and if that’s the case no need to back it up.
But recently i found out that it does store data that is not stored anywhere else, and that is tagging and storage profiles. If you are not using any of these you really dont need to back it up, but if you do, or if you use vCloud director (which uses storage profiles) it is very important to back it up.
This KB describes how to backup and restore the inventory service.
Another thing i found out lately, is that the inventory service uses a xml db (x-hive) and sometimes it can become corrupted (search will error / timeout). In that case you should restore the db or reset it.
If you dont need the data in it , because you dont use tagging or storage profiles, you can just reset it, the process is described in this kb , and quite easy to implement.