Is there any advantage to using it if the robot doesn’t run out of battery in a typical match without it? Is it worth the extra weight (~1lb)?
I would say that the primary advantage of the power expander is the ability to distribute the current draw from the motors across two batteries rather than one. If all ten motors are lifting heavy loads, then one battery will not be able to sustain the current output required to keep them all functioning at full power. If you are having current draw problems, then the power expander is definitely worth it. If you aren’t having any problems, then I wouldn’t worry about it.
I think Pastoral_Invasion hit right on.
This year, I’m not 100% confident a power expander will be necessary for most teams, as most bots will either being drawing lots of current driving (normal match play) or lifting (hanging). This is different from last year, when bots were required to have a fast chassis and a powerful lift. A lift simply carrying itself and an extra 2-3 lbs to lift the realistic max number of scoring objects (1 large ball + 3 buckyballs) should not draw an enormous amount of current to the point where a power expander is needed. At the end of the day, deciding whether or not you need a power expander should be played by ear.