Before Kimball goes to the dam the Boomers and BoS have to be dealt with. Without the Courier to deal with them Kimball would not visit the Dam. The stalemate between Legion and NCR at the dam will come to ahead when Caesar dies of his
The Boomers and Brotherhood, if neutral, are a non-factor in the upcoming battle and Kimball's visit. The former could make a good ally, and the latter is more of a potential long-term problem best tackled sooner than later. Kimball will comer regardless of their presence (and most definitely get killed). There's also no "stalemate" between NCR and the Legion; Legion's winning, hands down. By the time the Battle for Hoover Dam begins, not only will the Legion have caused all sorts of problems with their various moles, but they'll have used their Omerta allies to effectively wipe Vegas off the map.
Benny/Yes man..
Benny Shoots the courier dead. Returns to the L38 with an unkowing Mr House, tell him he 'somehow' retrieved the chip from some 'raiders'. House upgrades the securitrons and sends Benny off to the Fort. Caesar does his usual thing of trying to get Benny to blow up the S. Vault. (As the doors are indestructible apparently) Benny obviously upgrades the Securitrons there, tells Caesar he helped him, gets sent back to house, kills house, installs yes man. He then waits for the battle to starts, sneaks his way into the operations center in the dam, powers up the securutrons army and then Securitron Mk11's stomp the bejeesus out of the Legion, send the NCr packing..
Simples.
If any of that was possible (which is questionable), then Benny could have easily done all that whether or not the Courier survived. In fact, if any of this was possible, Benny wouldn't even need to kill the Courier; all he would need to do is just let the delivery go as planned.
Sometimes, I do wonder if his plan could have gone off without a hitch if he hadn't tried cheating...