Under normal circumstances it appears that this option does NOT provide the user with anything that he couldn't have done by simply doing a 'shift-select' to unselect bodies that he may have selected unintentionally or perhaps it was easier to just select all of them and then deselect the few that he didn't want to delete. However, there is one scenario where 'shift-select' does NOT work.
Starting in NX 7.5 when a function allows you to select more than one BODY, such as when selecting the tool bodies in a Boolean operation, we added an option to define a 'Selection Intent' rule, in this case the options are 'Single Body', 'Feature Bodies' and 'Bodies in Group'. Now let's say that you've got a bunch of bodies that you want to delete using the new 'Delete Body' function but some of them are members of a Group or they're part of a single feature, like a multi-profile extrude or where a Boolean subtract has resulted in multiple bodies, and after selecting all of the bodies with the intention of then deselecting the ones that you want to keep and it turns out that these bodies are either members of a Group or were the result of a multi-body feature, using 'shift-select' it's not possible to deselect all of the members of these Groups or multi-body features using a single gesture, however if I had an explicit command where a 'Selection Intent' rule could be applied than I could deselect the bodies that I wanted to using a single gesture. Now rather than develop a new 'gesture' just for multi-body deselection or even attempt to modify the current geature (after all, what if you really did want to deselect a single member of a Group) it was decided to add an explicit second dialog step, 'Select Body to Keep', where the 'Selection Intent' rules do apply.
Now it's possible that in the future we may add one of these optional second dialog steps in other places where you can select multiple bodies and where you might like to deselect some of them taking advantage of the 'Selection Intent' rules. And this would also address another issue, and that is that while 'shift-select' has become the normal way to deselect most anything in NX, it's not the most 'discoverable' function for new users. This explicit option would address this while still allowing the more experienced users to use a gesture to deselct objects since even though the new 'Delete Body' function has incorporated this new option, if all you really wanted to do was deselect bodies without any regard for their Group membership status or whether they're part of a multi-body feature, 'shift-select' still works just fine.
Anyway, I hope this helps explain why this apparent redundant step was included in the new 'Delete Body' function.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA Siemens PLM: UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
