Every file at once with Showall and Branch in Disk Sort
Press S in Disk Sort by Zaweba to list every scanned file flat, or B for the open folder and all below it, then tag, sort and act on the lot.

Two single keys change how Disk Sort by Zaweba lists files. S switches to Showall, a flat list of every file in the scan, or on the whole drive. B switches to Branch, a flat list of the open folder and everything below it. Esc takes you back to the open folder. In both lists, all the tagging and file actions work just as they do in a normal folder.
Why flat lists help
Folders are good for storing things and bad for comparing them. The biggest file on a drive might be six levels down in a folder you'd never open. A photo shoot copied from a camera can be split across a dozen numbered subfolders. A project might scatter its exports across many places. Looking folder by folder, you miss what's obvious once everything is in one list.
Flat lists remove the walls. Sort by size, and the largest files on the drive or in the branch rise to the top, wherever they live. Sort by date taken, and photos from many folders line up in the order they were shot.
Branch for a part of the drive
Branch is the one you'll use most. Open a folder in the tree, press B, and you see every file inside it and inside every folder below it.
It's ideal for a photo folder organised by month or by event. Branch on the year folder shows the whole year as one list. Filter it to pictures, switch to thumbnails, and you can cull a year of photos without opening a single subfolder.
It's also the quick way to answer "what's big in here?" Open a heavy folder that the size bars pointed to, press B, sort by size, and the culprits are at the top.
Showall for the whole scan
Showall goes further and lists every file in the scan, or across the drive. It's the broadest view in Disk Sort. Sorting it by size gives you the largest files anywhere, and sorting by modified date shows what has changed most recently, which helps when a drive has filled up suddenly.
Because the list can be very long, narrow it. Pick one kind of file, such as video, or use a name filter with Ctrl+F and the * and ? wildcards. A Showall of videos sorted by size is one of the fastest ways to find space on a typical home PC.
Acting on the list
Everything you'd do in a normal folder works here. Tag files with T and move on, or tag everything shown with Ctrl+T. Copy with C, move with M, rename in bulk with R or F2, zip with Z, or press Del to send the selection to the Recycle Bin after a confirmation showing counts and a preview.
That makes a few jobs simple. Gather every video from across a drive and move it to a second drive. Find every file over a certain size and decide on each. Pull all the photos from a shoot's subfolders and export the keepers with their edits.
Avoiding mistakes
Look at the folder column, or the info panel, before you delete from a flat list. Two files with the same name from different folders may be quite different things.
Remember that protected folders stay protected. Windows, Program Files and the root of a drive are blocked from changes even when their files appear in Showall.
Use Esc when you've finished. Going back to the open folder makes it clear you're working in one place again, which avoids acting on more than you meant.
In Disk Sort by Zaweba, S and B are two of the most useful keys to learn early.