I have a leaking radiator which I intend to have repaired. After reviewing the RAVE CD it says not to flush the system under the section on 'draining'

Can anyone explain why I shouldn't flush the system? Has anyone flushed theirs with problems/nil concerns?

My car is a Series 1 Disco with 3.9L Auto...

I just dont want to stuff something whilst trying to do the right thing considering I have been using a mixture of tap and distilled water to top up the system...

Cheers