For Wild Card, I mean. Think about it for a moment, after activating the El Dorado substation it's confirmed that Vegas is resource independent from the dam, and by destroying the dam itself you deprive the NCR and the Legion of their major goals in securing the region. That pot of gold everyone was fighting, suffering and dying over just got thrown off a cliff. Assuming the player upgraded the securitrons, Vegas itself has a very solid defense force but the Courier (and anyone who comes after him) or Yes Man don't have a gigantic army to control and patrol the Mojave. The Mojave itself is truly free. Just a thought for those who like to go for an independent Vegas.