- Windows Explorer has an option, which I've always thought should be enabled by default, named "Use check boxes to select items". (In newer Windows versions you can also enable it for the current view using the "Item check boxes" option in View > Show/hide.) Having that same capability available as an option in WinSCP's file browsers would be extremely handy, when needing to select lots of files for transferring.
- I don't believe there's any equivalent in Windows, but the GNOME Nautilus file browser on Linux has a preference, "Expandable Folders in List View". Enabling it effectively creates a single-pane tree view that mixes directories and files together, allowing you to explore everything beneath the current path in a single tree.
Personally I find it far more useful than the split view, which has two problems (IMHO): directories are redundantly visible in both panes, and you can only see the _file contents_ of a single directory at a time.
With a Nautilus-style tree view, the pathbar at the top of the view would still be useful, as would both entering subdirectories and navigating upwards to a directory's parent. (The pathbar would display/control the "root" of the tree, and directory navigation would change that root.) In the current 2-pane tree view it's sort of redundant, as the directory tree shows the same information as the pathbar.
As an example, here's a directory tree displayed in the WinSCP 2-pane tree view:
Here's that same tree in Nautilus' expandable tree view:
A single-pane tree view is especially useful when you need to select multiple files scattered across different directories, as you can expand them all and select the files all at once.
That situation is also where selection checkboxes become especially convenient. (So it's a bit annoying that Nautilus doesn't have those.)