WordPress MU

Can someone explain to me what the advantage is of installing wpmu in a subdirectory form like myblog.mydomain.com?
Is it only to have a sweet URL?
On install wpmu said it is adviced installing it that way, but why? Am I missing any features or can I expect any errors in the form of mydomain.com/myblog/
The problem is that I need Google Maps in my Blogs and the API key allows only one key per domain name...

Can someone explain to me what the advantage is of installing wpmu in a subdirectory form like myblog.mydomain.com?

Makes your clients feel that they have their own website instead of just being a knob within a larger site. Easier to remember URL. Seperate yourself from other clients who may not share your thoughts and ideals. Improved seach engine spidering over subdirectories. (As much as Google says it prefers subdirectories, it does take subdomains as seperate sites.)

As to the 1 domain name only, mydomain.tld is just one domain name. Anything in front of mydomain is a subdomain. Works fine for me with Urchin/ Google Analyics.

Good point about gining them the feeling about having an own domain name.
Unfortunately subdomains don't work for a Google Maps API key.
I just tested it, works for subdirectories, but no subdomains..

which plugin did you use with mu.wordpress to get google maps working?