[TMF]

Originally posted by quant
but I suppose bonsai filters only based on the item title

You can filter almost against any aspect of the database with Bonsai filters. I think ShadowPlan outliner was also good in this respect.
Btw. MLO mentioned above, will have this soon.

Is is that crucial to see the tree structure for the items matching filter in the search result pane?

It certainly helps, sometimes a lot.

You can navigate the search result pane, see given item's parent's, children, open it in new tab, rerun the search etc.

UR is flexible and one can do a lot of things. The thing is, if you do this often, are you going to bother, or are you going to use something better suited for that particular functionality?

Can you give an example or explain when having a filtered tree is a necessity for the problem at hand, so that I can better understand its usefulness?

I can't speak for others, but this is not about necessity.
In same manner, I could have asked "Is it necessity to use UR, when I can as well store all my text snippets in Word", but I didn't and purchased UR, because it works smarter.
For me, tree filtering is about working smarter, quicker/saving time, and having a better visual grasp of the situation, and avoiding confusion.

I don't have time to read whole thread, just would like to add my vote for the tree filtering.