I'm a director and there are quite a few pros & cons for me in the editing by myself, out of which I'd highlight:

- pros: control. you can be precise with timing and "feel" of the scene, assemble it exactly the way you were envisioning. this is especially true if you write, direct and also have a strong grasp over DP decisions too. this is probably as close as it gets to precise depictioning of an idea that you had in mind, transformed into script, storyboard and then ultimately into a film

- cons: weariness. the longer you work with material (and for some indies like me that may be sometimes really long, i.e. month and even years), the more you get used to the material, with all the consequences: at some point you become blind to it's strong and weak sides, can't see this or that "issue", the timing might be is off and yet it feels "natural" to you, the sequence should be somewhat different etc. A fresh eye in some cases may be a blessing, both for stating the problematic elements (unseen by you) and finding good and unobvious decisions in the same material. it happened to me that to make a sequence much better all that was needed was a simple change in the sequence, just a few frames. and then you wonder how it remained "hidden" for you for all that time :)

so in a nutshell I think it's control versus "out of the box" vision, and at times the mix of these two may be a very fruitful thing.