OK, even with the jumpers bridged, you may still need the blue power module – but not because of limited USB current. The ‘push-Button’ module seems to be designed to only work with power flowing through it. Unlike the dimmer it will not take power from the Arduino. This means for projects like http://littlebits.cc/projects/hold-an-on-off-state , the power module can’t be moved anywhere else or the button can’t be used. As a visual setup, having the power enter the circuit through a switch seems very misleading. It implies you’re cutting power to the Arduino when the button is pressed, however it’s obvious this is not happening.
I honestly think the Button module has a design error, this seems very limiting, or I might be doing something wrong. Regardless the justification above that every circuit needs the blue power module seems to fall flat when we have it entering this circuit using a switch.
So, although the USB jumpers work great for keeping the Arduino board powered and connected to the computer, you may still need both solutions. Without using the jumpers the board turns on/off more frequently messing up the port connection.