The default email address to use for your bookmarklet, so you don’t have to enter your email address every time. You’ll have an option to use a different address if you change your mind for a particular item. (Including your email address here just puts it into the bookmarklet that you generate here and save to your browser. The address is NOT submitted until you actually use the bookmarklet on Amazon.com to create an alert.)
Optional: if you want to default to a price alert that’s 90% of the current price, enter 90 here. Valid values are 1-99. You can always override the default while creating your alert on a case-by-case basis. Using a default saves you from needing to fill in a price when the default is appropriate.