Of all the CADGES, Dr. Light is the only one that really serves a purpose.   I don't mean that he plays any role in the games - quite the contrary, he rarely appears and when he does it's to give smartass answers to Mega Man's brain-damaged questions in Mega Man 7:

Mega Man: I just got the "Bullet Shooter."  That shoots bullets, doesn't it?
Dr. Light: That's right.  Don't forget that the bullets may hit things.

So in the games, Dr. Light is pointless.  But for sarcastic webmasters, he's indispensible.  Just as I need to be able to refer to Dr. Wily in ranting about all the evil robot masters, having a name to substitute  for "Mega Man's creator" is a real lifesaver.  Sadly, this is about as useful as the people on this page get.   Keep reading only if you're dying for a brush with lameness.

Rush sucks really bad in Rockman & Forte (see the Bonus section), but he wasn't always quite that dumb.  In other Mega Man games, he actually serves valuable purposes, like transforming into a jet-scooter, which lets you bypass thousands of voop-voop disappearing blocks .  In a couple games, he can perform a Gospel-style fusion with MegaMan, called the Rush Power Adaptor, which is generally unhelpful (I'm pretty sure that it actually lowers Mega Man's versatility and strength) but looks pretty damn neat.  This is especially important in Mega Man 7, where you can face off against Forte and Gospel, before their own fusion was perfected - for a brief, shining moment, Mega Man and his dog looked slightly cooler than their rivals.  See the Bonus for more information.

Even as Dr. Wily was giving mechanical life to his lighters, deoderant, et cetera, Dr. Light was taking a more practical approach to his pseudoanthropomorphism: why not a robotic briefcase?  The fact that Mega Man already apparently had the technology to haul around fifty thousand robot accoutrements was apparently lost on the Doctor, and so he ended up reinventing the wheel by creating Eddie.  At least, that's my main theory.  It may also be that Eddie is a refugee Hard Hat Harry, seeking anonymity by hiding under a trash can - fate keeps screwing him over by sticking him in combat zones while the trash can contains valuable robot supplies.  Either way, all Flip-Top did was appear at set locations in the game to give you power-ups.  Nothing about this couldn't have been accomplished by, I dunno, just having the power-ups be there like every other power-up in the game.  Eddie is an extreme CADGE.

Beat was conceived in a desperate bid to add some degree of depth to these stupid games; whatever game it was that he showed up in had letters strewn about (ie, a box with "B" or "A" in it), and if you collected all four, you could gain access to a new superpowered attempt to capitalize on Duck Tales mania.  This cereal-box game design theory was undermined by how completely stupid the whole thing was, especially the prize itself.  For finding a bunch of dumb little monograms tossed around the game, I should at least get something cool like the Rush Power Adaptor (which was useless, but neat-looking).  I don't really remember what Beat does - I think it's something dull like yanking you out of bottomless pits every so often.   Maybe he only does it three times.  I'm not sure.  It seems like kind of a shortchange miracle; let's face it, would it really ruin the game balance to let me earn something that saves me from the pits every time?  Beat is just stupid.

We all knew Dr. Wily wasn't really keen on the idea of customization and universal applications - after all, he builds a separate android to house each and every moronic concept for a weapon that enters his fevered brain.  But I was kind of hoping that Dr. Light would understand that if he had some new idea for a robot powerup, he could just incorporate it into the existing Rush system.  No go; the good Doctor also suffers from this obsession with creating unnecessary robots, and, at great expense of time and money, produced the pointless, not to mention highly goony, Tango.  I'm not exactly coming out in support of Rush here, but since the stupid dog exists, he might as well be used.

On the other hand, there is something to be said for having backups.  For example, after Dr. Light built Mega Man, he realized he might need another robotic operating buddy should his original creation fail.  So he created Proto Man, who apparently got hit on the head, lost his memory, and joined the enemy, or something...I don't really remember the plot of Proto Man's first game.  But anyway, after that, Dr. Light had to create another backup warrior.  So here we see the furious, fatal samurai Rightot.  Until the day Mega Man is finally wiped out, though, Rightot is content to play the role of merchant and wacky comic relief.  Unfortunately, the market system in the later Mega Man games is another CADGE-like addition, and the comedy isn't funny, so Rightot ends up just being a loser.  So he fits in.