I have been a Technology Director in law firms for 25+ years. There are MANY reasons one would not want to delete ALL files in the trash. Those of you who've posted your condescending comments about "don't store things in the trash" simply show your OWN ignorance; you're not serving to put the person who posted the question down as it is a perfectly valid question.
Here are the two reasons I need to selectively delete items in the Trash:
1.) Attempting to EMPTY the trash bombs repeatedly. Mac OS does not inform me which file it is giving up on, but the rest of the files in the Trash bin won't delete because the Mac OS is evidently having difficulty with just one (perhaps corrupt) file. So I'd like to SKIP the file that's having problems and try to selectively delete several files / folders at once until I find which the culprit is.
2.) I am working on a computer that is not my own. I am a Tech Support person. I have deleted items that I wish to remove from the Trash bin, but I do not want to make the judgment call as to what files or folders the person who owns the computer may or may not want to delete. (He's a doctor who is with patients all day and then out of town for a week, so I do not have the capability of asking him at the moment.)
3.) Being a supporter of Windows (and DOS before that) since the inception of the microcomputer, yet not being familiar with Mac OS, I did not know how to permanently delete any files or folders WITHOUT moving them to the Trash bin first. (Now I know, thanks to a couple of the responses above). So, unfortunately for me, I deleted several hundred GBs worth of data from an external USB drive that I was given to "back up" the Macbook I'm working on (that's about to die permantly due to impending hardware failure and overheating). So there is over 100 GBs worth of data in the Trash bin that I DO NOT want to back up. And because I have already backed up most of the hard drive, the external drive is nearlyl full and I therefore cannot "Restore" the data to its original location and use the steps mentioned above to permanently delete the data from its original location because there is now insufficient space to do so.
4.) I do not want to back up the Trash bin which will take up too much room on the external drive. Because the Empty Trash utility won't remove the items in the Trash bin, I need to remove as many of the files as I possibly can before backing up, even if that means I wind up with one corrupt file remaining in the Trash bin.
So... those of you above who've so arrogantly stated there's no reason you'd ever need to selectively remove files from the Trash bin, perhaps before putting others down, you might want to think about how that makes YOU look -- not the other person you're trying to look "smarter" than -- before you post on a forum viewed by potentially upwards of a million people who now know just how small minded YOU are, not the person you attempted to belittle.