Answer 1

May be your question is incomplete. Although, "CLEAR" property is not relevant to the the designer choices but very important. i.e you can/must use it when you used "FLOAT" property to the previous element. This property [clear:both/right/left;] just force the current element to clear the previous element's "FLOAT" property and take a line break. This property is very important to design the better layout of the page as your webpage may looks different from the layout you thought.