wheel - 12:59 pm on Mar 23, 2011 (gmt 0)
If you're being 'offered' domains, that's not because it's good for you necessarily. It's because they're probably in the business of selling you domain names. You're a good example - you've bought domains for no apparent good reason :).
Two reasons I would use these specific names. One is for type in traffic for specific terms or products. You can put up mini-sites for very narrow niches.
And the second is as you mentioned, it prevents others from getting the domains. I believe keyword rich domains are getting more valuable over the years.