Note: You do not need to be connected to the Internet to log in to your PC when you turn it on--assuming you use the Microsoft account login feature. You can even disable the requirement to enter a password (you do so in the PC Settings Users screen), but you'll get a warning if you do this.
Only enable this if you're confident no one else will be using your system. If other people do, they'll have full access to your Microsoft Store account, your SkyDrive, and other shared features.
Benefits of a Microsoft account
Being connected to the Internet and logging in with a Microsoft account gives you several benefits. First, as mentioned earlier, you have access to your SkyDrive cloud storage. If you have other PCs, smartphones, or tablets, you can access SkyDrive from any of your Internet-connected devices. This feature saved my bacon during the course of my work at PCWorld, allowing me to send my editor a critical file using SkyDrive on my iPhone.
Every Windows 8 user gets 7GB of free SkyDrive storage. If you exceed that amount, you have to pay an additional, ongoing fee. However, 7GB is fairly substantial, provided you're not storing tons of high-resolution images and video.
You also have what's known as "single sign on." You no longer need to enter your account info when you go to the Microsoft Store, the Music store, or other features. You'll be able to sync your main PC's settings with other Windows 8 PCs you may use, provided you can log in to those PCs with your Microsoft account. So it's easy to keep your Windows 8 laptop and Windows 8 desktop in sync.
Drawbacks of a Microsoft account
As useful as a Microsoft account can be, there are pitfalls to using one, too. SkyDrive itself has some odd limitations compared with similar services such as Dropbox. SkyDrive imposes a 2GB file size limit, which makes uploading large, high-definition video files problematic. Also, Microsoft has reserved the right to monitor what you upload, and if it thinks what you've uploaded is illegal, you'll find those files deleted. If that Big Brother aspect of SkyDrive troubles you, you may want to consider other services instead.
SkyDrive on the Desktop
A Windows 8-style SkyDrive app is included with your Windows 8 installation, but how do you get to your SkyDrive folder from desktop software, like Microsoft Office? If you use the Office 2013 preview, you're asked for your Microsoft login, so you'll automagically have SkyDrive access. But other apps might not be so smart. In addition, you may simply want to copy files between local folders and SkyDrive. While you can do this with a Web browser, that's a cumbersome process at best.