"As far as I'm concerned" is simply opinion. When someone says this, they are expressing their opinion on something. In my opinion, this statement also implies that the person acknowledges:
1. Their opinion is solely based on the knowledge (or limited knowledge) that they have on a situation.
2. They acknowledge that they probably don't know all the facts surrounding the situation, but they don't care to know all the facts. They are content with their opinion, and their concern doesn't go beyond this.
I hope this helps <3