What do you like best?
Very easy to install and use. There's a free version which allows you to see the results of the disk scan in a tree format and allows you to sort based on size, %, number of folders, etc. You can delete files/folders from directly within the user interface as well. The scan for the disk goes very quickly and you can scan multiple disks if you have them. I haven't used the Professional version but apparently you can get reports, do automated file cleanup, and search for duplicate files (which would be very nice). The installer file size is also small, which is key if the computer is already very low on disk space.
What do you dislike?
The tree view can get pretty busy when diving down within a folder. Other than that I really don't dislike the software at all, especially since it is free.
Recommendations to others considering the product
Start with the free version if you use need something to find out what is taking up so much space on your hard drive.
What business problems are you solving with the product? What benefits have you realized?
The software that we use on a daily basis can take up a lot of hard drive space so every once in a while we make sure to run TreeSize to figure out if there are files we can delete, archive, or move to a cloud/server location to free up local hard drive space. Moving 100% to the cloud is not an option for us as there are many times we have to have the files locally due to network unavailability at a client's site.