No, it is not always necessary to use design patterns, but it has been agreed a long time ago that using design patterns will generally improve the quality (including both development and operational aspects) of the produce.

Most often there is no way to 100% sure about the "best" design pattern; usually a number of relatively good alternatives exist. Of course there are some occasions where a dominant pattern exists and few designers even try to think of alternatives.

Lastly, no, using design patterns is not just about clarity/handiness. It's also about the quality of what comes out of the tube.

It seems that you've been reading about UP (initiation and elaboration)... Keep on reading but remember that the most important lesson to learn is what you can leave out from the complete package - what is relevant and what is irrelevant for your particular project.