What is teaching? In general, the student gets instructions, guides, tips etc. from the teacher, processes them, understands them, up to some extent, then practices. The process of practicing is in a way self-teaching.
The one can get the instructions from various sources, with all means that we have today, books, internet, CD’s etc.
Self-teaching in my opinion is a great activity, it develops things like observation, awareness and so on… In most of the cases self-teaching is kind of a back engineering, for example: the one hears a music piece and then try to find out how it is played, what kind of skills need to be developed in order to play that music…
A good self-taught guitarist in most of the cases is perfectly aware of what they can do and what they don’t know how to do. They know very well when they need a teacher’s help and for what.
In my 30 years experience of teaching guitar I have seen endless number of people which proves the above.
From other hand having a teacher or instructor safes time and the process of learning is more fluent.
If you are planning to teach yourself guitar check out those online courses. I designed them especially for adults.