It means you have to know where you're going before you start. If you don't, you'll degrade into producing rewrites instead of adding requirements. One of the means for keeping tighter control on the software while enabling continuous change is to produce a software build at least weekly, if not daily. This requires the software to be assembled, available, and accounted for constantly, so that rapid responses to issues are possible. The longer the time stretch between builds, the greater the opportunity for confusion and mayhem.
Constant coordination is needed between developers, testers, and users.
And source and version control with complete configuration management is crucial among developers. A rapid-fire schedule is unforgiving, and frequent releases are uncompromising. It's either happening or it's not. Let's admit it. Time-boxing and rolling releases are just formalizations of what the market is forcing to happen.