Set to value to Not Available to cause the rule to become invisible to the rule resolution algorithm for all users (including yourself), and to bypass validation of non-key fields. The Not Available setting is useful in experimentation and troubleshooting to assess the effect of two rule versions.
Set this value to Withdrawn so that the rule is never selected by rule resolution. In addition, a withdrawn rule masks from rule resolution any other rules which meet all of these tests:
The other rule belongs to the same RuleSet
The other rule belongs to the same major version of the RuleSet, but a lower minor version or lower patch version
The other rule has the same Applies To class (if relevant and other key parts match)
If circumstance-qualified, is qualified with the same circumstance type and value.
I think you are confusing Blocked and Withdrawn in your reply. Blocked results in an error. Withdrawn does not necessarily result in an error if an alternate version is found according the algorithm that Santanu correctly described.