I found a really informative webpage about why you should brown meat before incorporating it into stews etc. I've always wondered why recipes insisted on browning the meat, and assumed there wasn't much logic to it. But as this gaudy but really educational page describes, it's for a very specific reason - to cause a reaction to occur in the meat (the Maillard reaction) which improves the flavour, and which would never have a chance to happen at any other point during the cooking.
I tried it while making a very nice lamb tagine, and the results were very nice indeed (Philippa thinks so too). It's a very nice recipe anyway, actually - loosely based on this tagine recipe but with prunes instead of sultanas, and generally a little less faffing. Highly recommended recipe.