Its a form of marketing. Technically you shouldn't be blindly clicking away seeing how you are "suppose" to read the terms and conditions.
Not to say I approve of it but I never install anything "Automatically"
As much as I'm good at avoiding these things, it's still unnecessary. I really shouldn't have to take the extra steps to read every single button and checkbox to get as little bloatware as possible.
Should go:
Intro screen with just next/cancel buttons.
Terms and conditions. Agree/Cancel buttons.
Install options. Such as language, path, shortcuts, and any add-ons the devs feel necessary to include. Next/cancel buttons.
Done.
None of this [Default checked] Yes, I want to install Gamespy so I can play with my friends online.
Or even
"Look at this stuffty toolbar, click agree to install it, click disagree to continue installing the program you want"