Van:

I believe we use legacy (since some of our machines have older ACAD).

XCLIP:
This command works only in MS and on XREFS.
If you create a closed polyline around the area you want to see, XCLIP will 'trim away' everything else, keeping what is inside.

The down-side to this is that you can only have one in a drawing.

2D Drawings
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This is handy for 'cut-aways', for example, if you have an elevation view of a pipe rack, you can use XCLIP to outline your (and step) your pipe.

I also use it to streamline my elevations. For instance, if I want to show a North and West elevation of a building, I draw an 'L' shaped closed polyline encompassing the North view and the West view. Now my 3DCLIP works better since there is less 'clutter'.

Modelling
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Helps when I have to model in complex areas. I can just clip away the information I don't need, IE. modelling in on the seond floor of a 4 story building.

Does this help?