You'll be able to clean the insides of both dip tubes if you have a little brush. you'll be able to get any sticky syrup off the threads for the posts, and you'll be able to clean and lube the poppets and safety valve.
clean, lubed poppets and valves are less likely to leak than if they are dry or dirty.
I clean my kegs every so many re-fills. otherwise, I just clean with oxyclean, then sanitize until I have beer to fill it with.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10