Charisma is a Force Multiplier
Sometimes, people talk about charisma as just a positive—for instance, a lot of generic self-help or business advice assumes that charisma is generally good. On the other hand, you sometimes see people, often from “nerdier” communities, who say charisma is bad, an arbitary and unfair advantage, just a distraction from the facts, etc. 
I like to look at it from a somewhat different perspective. Military strategy sometimes discusses the concept of “force multipliers”—factors (often technological or strategic) that multiply the effectiveness of equipment or personnel. For example, precision weapons guidance is a force multiplier—if it takes dropping twenty normal bombs to hit a target but only one guided bomb, the guidance system could be considered a 20x multiplier on the effectiveness of your bombs. 
Perhaps the greatest force multiplier I am aware of for “normal situations” is charisma. Charismatic individuals are more likely to be effective and successful at a wide range of social tasks, more likely to influence broader planning towards their goals, more likely to elicit support from others, and so on. I would suggest that charisma is not another skill that’s a useful addition to a broad range of skills; charisma can be a multiplier for all or almost all of an individual’s other skills, at least insofar as the application of those skills involves working with others (and more skills do that than you might think)!
However, there is another important factor that should be taken into consideration. The fact that charisma can be such an important multiplier means that, if an individual’s impact is negative, a more charismatic version of that individual will likely have a substantially more negative impact. 
Some of the most harmful results I’ve noticed in organizations and communities have arisen from very charismatic individuals who nevertheless pull the group in the wrong direction. I should note that I’m not saying that these individuals are necessarily malicious, evil, or similar—my view is that charisma is a skill like many others and not intrinsically good or bad.  However, one doesn’t need to be malicious to be destructive—an appealing, persuasive person with the wrong take on what strategy to pursue can be very costly for an organization or community.
As such, I recommend exercising some degree of caution when looking at charisma and charismatic individuals. I think the frame of charisma as either a bonus (as in the default view) or as a minus (as in some of the “nerdy” views) is misguided—instead, I find it helpful to view charisma as a multiplier and to plan accordingly. In most cases, charisma’s impact is contingent on what the individual would otherwise be doing anyway—and while developing charisma can certainly be useful, if someone is pulling in the wrong direction charisma will likely make that pull stronger.
This also of course applies to oneself. The more charismatic, persuasive, etc. you are, the more you may need to worry about having an undue influence on those around you, and the more care you should take to ensure your powers are used for good and truth.
 At one point I considered something similar to this—the view was something like “If you had some way to 100% reliably persuade someone of whatever you wanted, that would be mind control and hence unethical. However, the use of normal methods of persuasion aside from the facts is just a less reliable form of mind control, and therefore immoral.”
 The actual values for this are in all likelihood not just 20x but very considerably higher. Strategic bombing with unguided weapons is much less effective than many seem to believe; the massive aerial bombardments of World War II, which led to the deaths of many civilians and aircrew on both sides, are now often considered to have been wasteful and broadly unsuccessful at achieving their objectives.
 An obvious exception exists in the case of people whose impact is negative because they are very uncharismatic.
 In my view the stereotype that exists in some nerdy circles of charismatic people as inherently slimy/manipulative/otherwise not to be trusted has been very negative, both because I do not consider it to be accurate and because I think it discourages people in those communities from themselves developing charisma or related skills.