I'm sure someone will correct me if I'm wrong but here goes.
Your stereo receiver pumps out 100 watts/channel, 200 watts total into Left and Right.
Case 1
You have your speakers connected to the A holes (ha ha) with the jumper in place on the speakers. In this case the woofers will use what they require and the midrange and tweeters get the rest. (100 x 2 = 200 watts total)
Case 2
You remove the jumper on speakers. You connect the midrange/tweeters to the A hole, and you connect the woofers to the B hole. Now your midrange/tweeters will get 50 watts/channel, and you woofer will get 50 watts/channel. (50 x 4 = 200 watts total). I think if you do this you will not be happy with under powered woofers. Could the amp start clipping in this scenerio - I do not know. Someone might though. Maybe a sophisticated receiver will divide the power judiciously, I do not know.
Did I help/hinder/confuse/annoy you?