Often, choosing which side of a wirecut to keep costs time and effort because there’s no key bound for flipping, AFAIK.
I find that it’s easier and quicker set the “KeepAll” option set, and then when I make wirecuts, I just make the cut, and just delete the pieces I don’t want. This method works well for doing miters.
The invert option switches the highlighted part that will be cut away.
Hi Brenda - click the mouse in the viewport to see the possible results highlighted - Enter/Right-click when you see the parts highlighted that you want to delete.
-Pascal
Thanks for that tip Pascal. I never discovered that. 
Dan
Hi @pascal,
feedback color when rhino asks for the cut depth point is still black. Can this be changed in the future please ?
thanks,
c.
Got that, thanks. Input curve color would be the expected color I guess and not official ‘feedback color’, at least for the displayed copy of the curve.
http://mcneel.myjetbrains.com/youtrack/issue/RH-31989
-Pascal
Yep, i´ve meant it should look like when doing an extrusion of the curve. 
c.
When doing mitres, I find it quicker to chop both parts at once and delete what I don’t want.
fwiw, i also do it the way you’re describing.
Check out a clever plug-in called Peter’s Tools which has a handy tool called Temporary Straight Line Trim. You just draw a line you want to trim against, press Enter then delete what you don’t want to keep…Sweet.