Its brilliant, and lets you use kits as a base, rather than the main ingredient. For example, I like to make up a stout with a small mash of specialty grains instead of buying a stout kit (unless doing a toucan) as below:
1.7kg Coopers kit (lager, draught, real ale...whatever).
1kg LDME
Sounds stock? Righteo, well here come the grains that'll transform it into a rich, chocolatey pint o'delight:
350g Crystal
150g Chocolate
50g Black Patent
Steep those grains in a few litres of hot water at 65'C (or even just bring to the boil from cold as slow as you can, while stirring) and you'll have the process done. Strain off the liquid with a wiremesh collander and flush the remaining grains with a few cups of hot water, adding all this liquid to the fermenter. Now top up and ferment as normal. Or, use a plunger as others have mentioned above.
It'll turn out a hellava lot better than your usual dark beer from a kit.
Cheers - boingk