I don't thnk its a necessity but it makes life a bit easier in the following circumstances.
1. When rain turns into sleet or snow and you don't have enough protected storage space.
2. When it's a downpour that is going to last awhile and you're hunkered down for hours. A little extra room to cook or move around is nice.
3. When the wind is strongly blowing...and you're pitched the wrong direction...the extra size tarp can be pulled around to block it.
4. When the sun is beating down on you and with a larger fly a great awning can be made with the Leki's.
Just my .02
Sounds like good reasons. I don't cook, so cooking isn't an issue for me. I can easily get away with using a small tarp, however, I do prefer a larger one.