Use of Mercurial hg bundle and hg export vs merging?

When exactly would you use hg export and hg bundle?

These commands are listed on the Mercurial quick start guide but we're not clear when to use them.

Currently we manage dev by having different repositiories and merging between them. Ie:

cd myapp-1.01
hg pull ../myapp-1.0
hg merge
hg commit
hg push

When would you use export and bundle instead of the approach we use?