The Enabled Tickbox will set the Rule 'live' when you publish the ruleset. If this tickbox is not ticked, the Rule will not run, even if the ruleset is published.
As an example in the following screenshot, the first rule will not run, whereas the second will:
When building your rules, you need to ensure that they are enabled if you would like them to run.
Unticking the enabled tickbox is a good way to 'disable' a rule without having to delete it.
Note you can only tick/untick this box when in draft.