I am learning Solaris Zones and I have the following doubts:

1.Sun has developed both Zones concept as well as Virtual Box concept. To work in Solaris if zones method is there, what is the need for virtual box?
From my little knowledge, I feel virtual box and the whole root zone are same except virtual box is gui oriented. please correct if wrong.

2.I am aware that sparse root zone just shares filesystems from the global zone and if the shared files are deleted from the global zone it affects the sparse root zone too.. please let me know in what situation a sparse root will be used and in what situation does a whole root zone be used?

Many thanks to you all ....