This worksheet is used almost exclusively by the children of very wealthy individuals (don't we all wish we were in a position to take advantage of it?) to see if the child's alternative minimum tax ("AMT") can be reduced and, if so, to figure the amount to enter on the child's Form 6251.
The purpose of this worksheet is to provide a benefit on a child's tax return, but only if the child has investment income over $1,400 in 2010 (see Form 8615) and is subject to the AMT. To be subject to the AMT, the child has to claim significant tax benefits from things like interest expense, charitable contributions, and depreciation.