Your receiver's bin has a built-in list of TPs-in-use for each satellite profile. Autoscan scans only this list.
Blind scan first checks for a readable signal on a frequency, and if the freq is "alive" then channels are scanned on that freq; the whole operating band of frequencies is scanned.
Most people prefer using blind scan (after deleting their channel list) as Charlie plays a game of moving around channels to different TPs. Autoscan may miss a few channels.