For me, it's convenience. My phone is laying on the desk, I can just stretch my hand, press the home button and instantly see the overview of situation. Easily distinguishable lines (courtesy of jailbreak and LockInfo) for missed calls, SMSes, emails, calendar events. What's more, unlike the default notifications, I get a little bit more information, allowing me to see that all the mails are from Facebook and can be ignored at the moment.

I don't cary my phone with me everywhere, especially when at home, so checking up on the situation is a common task for me.