DTerm provides a context-sensitive command line that makes it fast and easy to run commands on the files you're working with and then use the results of those commands. Command line work isn't a separate task that should live on its own—it's an integrated part of your natural workflow.
No matter what application you're in, no matter what document you're working with, just hit DTerm's hotkey and it'll be there for you, already set to the working directory of your current document. When you're done, hit escape or just go on about your work, and it'll automatically fade out, leaving your screen clutter-free.
DTerm also has a number of other features to make it frictionless to get in and get out of the command line, like the ability to insert your selected files or current document into the command line, copying the results of a command and dismissing DTerm, or browsing back through your command history and results.