Why is weight so important?

[MrForbes]

Weight is definitely very important. There are different ways of dealing with weight, though. If you start out with a realistic weight budget for different parts of the robot, and revise the design as needed to meet that budget, then you might be able to get away without having to do any "weight removal" machining at all. We did this last year, our robot was pretty big and capable and weighed 10 lbs under the limit.

There are some folks who seem to get carried away with making everything as light as possible, and they probably have a great future in the aerospace industry. Others don't really worry too much about spending any extra time making things light, and they probably have a great future in the consumer goods industry.