Disabling an OKR Authoring feature for a period prohibits users from adding new objectives, but you can add key results to the objective of that period.
The following are the reasons to disable an OKR Authoring, but not limited to them:
When a new period is added and objectives are frozen.
Let the users focus on OKRs of current period for time being, but you can go ahead in adding key results.
When any event relevant to the period is being postponed.
To disable Allow OKR Authoring for a selected period:
Similarly, you can enable the Allow OKR authoring for a selected Period.