A hypothesis is a basic building block that defines the idea around which testing campaign changes are created and evaluated. Any test in VWO previously required a linked hypothesis to bring a holistic understanding of what the testing campaign represents in terms of the idea that is being evaluated.
A lot of users create and manage hypotheses in other tools and may not be using VWO Plan extensively. For example, an organization that uses Jira to manage their workflow may not be inclined to maintain a duplicate set of hypotheses in VWO and update them manually.
To support such users, VWO will no longer enforce a testing campaign to be linked with a hypothesis. If you are not maintaining your ideas anywhere, it is highly recommended that you still create hypotheses and link your testing campaigns to them. Hypothesis-driven testing ensures that your approach to your experimentation program remains systematic and organized.