In some cases you may go to the effort of setting-up / configuring a skill but want to temporarily disable it from use by the bot; for example:
Whilst you're populating content.
The third party (Front Office, ServiceNow, Quickwork flow) is temporarily unavailable.
Configuring a ServiceNow or Front Office instance (for example) can be quite a bit of work, so you wouldn't want to have to do that multiple times if it was temporarily unavailable.
Example use cases:
We have a Front Office instance that automatically shuts down on a schedule to save hosting costs, so if someone tries to use the QA bot without turning the instance back on errors in the bot (and within the DevOps Analyzer) appear.
Moving between QnA versions (e.g. 4 to 5) - you need both skills to migrate content but wouldn't want them enabled at the same time for too long; this is on the assumption it's not done automatically by us on behalf of the customers.