After calling make installworld (or make world), there are two ways of updating source files in the new world: calling mergemaster -p or make distribution.  I know that mergemaster calls make distribution but what else does it do and why would I call it instead of just make distribution?
What does 'mergemaster' do that 'make distribution' doesn't?
freebsd;source;jails
make distribution just installs new configuration files, while mergemaster walks interactively over all config files and asks you which ones you want (and intelligently upgrades files you never edited in the first place if possible). It even gives you the option to merge them as needed. Basically, it automates the process of installing updated config files, doing all the diffs automatically and giving you a nicer way of merging the old and new config trees.If you're curious how it works, mergemaster is just a shell script.