When you click the "I like it" button on a photo detail page, that photo gets added to your Favorites list so that you can easily find that photo again at a later time. Also by "Favoriting" (you're right, it's not a word but since Oxford snuck "sexting" in when no one was looking we feel emboldened), you add to that photo's interestingness rating. Your favorites list shares its information with the Liked By function and lets others browse photos in interesting ways. You can't hide photos you've liked from everyone else, nor should you! Celebrate it!