[p4] Moving a changelist across to a new branch?

[Nick Levine]

I have to say: working solidly on a bunch of files for two weeks
without submitting anything sounds really scary. I appreciate that
often there'll be a policy of "don't check in anything that'll break
the build"; and that realising you need to copy everything onto a
branch after two hours involves the same issues as - but maybe less
work than - doing it after two weeks. What would concern me is the
thought of doing all that work and not having any intermediate stages
to fall back on. So I'm curious to know whether waiting for a longish
"logical change" to be complete before submitting is a common
practice?

- nick