Is Charisma a useful stat in Fallout: New Vegas?

Charisma increases your speech and barter score, and if your charisma is too low some interactions will not be available, regardless of your speech or barter skills. According to the wiki though, these interactions ultimately do not have any significant effect on game play, nor do they provide any special bonuses.

High charisma is also required to obtain the Ferocious Loyalty and Animal Friend perks. Ferocious Loyalty grants your companions a boost to damage resistance when you drop below 50% health, and Animal Friend will prevent animals from attacking you unless you attack them first. Something to note about Animal Friend however is this:

Deathclaws are not classified as animals for the purposes of this perk. Neither are any variety of arthropods such as radscorpions.

One final thing to mention is that it also increases companion nerve. Description according to the fallout wiki:

Companion Nerve gives each companion in the party +5% to their damage and armor, up to a maximum of +50% at 10 Charisma.

Charisma is only useful for 1 purpose in Fallout NV. Companions. Like fallout 3, charisma really doesn't affect anything since most checks are based on your barter or speach skill level, not your charisma. 1 charisma and 100 speech is the exact same as 10 charisma and 100 speech. Its better to max intelligence for more skill points to get your skills up to high levels.

Now, again the one thing that charisma does affect in NV that it didn't in fallout 3 is your companions armor/attack bonus, which is up to 50% at 10 charisma. This is a huge amount, making tough companions even tougher. This is usually only good if your making a non-combat character and are using your companions as the main meat in fighting. A 50% boosted companion can kick major butt even in very hard mode. So, 1 charisma is good for most games, but if your playing a non-combat character for roleplaying, etc max your charisma and intelligence for easier play.

Charisma i've found is actually very useful in Fallout New Vegas I highlight that because charisma is more useful (more specifically Speech) in New Vegas than in its predecessor Fallout 3.

The greatest advantage of a high charisma is the high speech skill that comes with it which can give your character more options/choices in-game e.g. convince someone to give you a better reward for killing someone etc.

The other great advantage is that the high barter skill is great for selling items to vendors because it actually increases the amount vendors pay for your items and reduces the amount you pay for vendors items.

Overall when I finished New Vegas I actually regretted not investing more into my Charisma (Speech) because I lost out on lots of opportunities in the game making Charisma very useful and a major priority if you're playing the game again with a different character.