By default, files are sorted clockwise by decreasing file size. From the View menu, you can set a different sort order.
The default. You can quickly find files that take away most of your disk space.
Allocated File Size
When opening an ordinary directory, this setting will produce a similar display as for the File Size sort order (since usually there is only a small difference between the file size and the allocated file size). When scanning a directory managed by a cloud service such as Google Drive, Dropbox or OneDrive, this setting will effectively hide all those files that are not currently on the selected drive but are downloaded on demand (since their allocated file size is 0 Bytes).
Directories are sorted by the number of subfiles, followed by all the regular files sorted in alphabetical order. Having a lot of (small) files may slow down some operations: for example, copying a directory containing many files is often slower than copying a directory with less files but the same overall size. With this sort mode you can quickly find such slow directories which you may want to exclude from a periodic copy operation or backup.