When I have a selection of several objects in Illustrator, and I want to align or distribute them, then Align to Selection is often (but not always) selected as default. Clicking on one of the selected objects, automatically turns the mode to Align to Key Object which is extremely handy.
Additional features for aligning objects are pretty well documented here.
Question: Is there also an easy way to switch the mode do Align to Artboard without using the selector in the Align Panel? I noticed, that sometimes Illustrator does exactly this by default, by I never managed to find out when this happens.