You can tear off DaisyDisk’s petals and drop them to the special area at the bottom called “Collector”:
In addition to drag-and-drop, you can put files and folders to the Collector by selecting the Move “Selected File” to Collector command from the item’s context menu, or by pressing ⌘⌫ hotkey while pointing to an object.
Don’t worry, the files remain intact until you click the Delete button.
You can expand the Collector by clicking on it to make sure you are not about to accidentally delete some needed files. The expanded Collector works just like the sidebar, so you can preview files and drag them out. Another way to get an item out of the Collector is to point and click the × button near its name
What can you delete?
Some folders like
/Library or current user’s home folder are not meant to be deleted, so the Collector will not accept them.
Semi-transparent (consolidated) petals also cannot be removed, you’ll have to expand the group and drag individual files and folders.
Clicking the Delete button starts deletion process, but you’ll have 5 seconds to change your mind and press Cancel.
DaisyDisk permanently removes files and folders instead of moving them to the system Trash, so that the disk space is actually recovered. These files cannot be “undeleted”, but there are other ways.
Free space not appearing after deletion?
Contrary to what you may expect, deleting files in macOS may not immediately produce free space. If Time Machine is enabled on your Mac (which should always be recommended), it will regularly back up your entire disk’s content in so called local snapshots. The snapshots are designed in such a way that they don’t consume additional disk space if there is little change compared to the previous backup.
So, when you delete a file, its copy may still be retained in the local snapshots, and still consume the same amount of disk space. In result, the free space will not grow, but the amount of hidden space, and more specifically, the purgeable space, will increase by the corresponding amount. This is normal — macOS will eventually automatically reclaim the purgeable space when the apps request more disk space. Alternatively, you can forcedly purge it with DaisyDisk.