Rule conditions allow you to test the state of another rule. This is an important feature that allows you to break down complex logic into smaller components that are easier to create, troubleshoot and test.
If you refer to other rules, Reactor does not check for loops/circular logic. That is, if rule A refers to rule B, and rule B refers back to rule A, that is a logic loop, and it could result in an "infinite loop" of evaluations. Be careful in setting up your logic to not create such loops."With great power comes great responsibility." --many