This Is Actually Pretty Neat
I copied my entities from Trenchbroom into it and realised that I had an entity with a targetname set to "". Oops! Like nathnolt said - you can use this to remove naming conflicts very easily if you plan to marge maps. Or if you are having signon buffer issues, this could be used to give shorter entity names. Or if you just want to change your names, you can do it very quickly with this.
This seems really useful.
In the long run this seems like something Trenchbroom should support internally. I believe Radiant would automatically rename targetnames if you copy/pasted. On the other hand, sometimes you don't want that. Maybe it needs to be a toggle.
One suggestion for a future release. Maybe checkboxes to select a given suffix style:
1. leading zero (e.g. -01 or _01)
2. append with a letter (e.g. -a or _a)
Along with an option to automate adding them. This would save people having to add by hand.