Okay, this one's huge: With MT4, everyone who knows how to make a Movable Type template also knows how to customize any Movable Type application screen.
Anyone who can create a template in Movable Type can now go
in and customize the Dashboard or any other page in the application
using the skills you've already got. And if you're new to MT, you can bone up on the Template Tag Reference documentation for a list of all the powerful tags available to help you make MT4 fit your needs perfectly.