Originally Posted by
Bullettime
He doesn't need to consult with Mueller, no. However, Barr is already surrounded by controversy for his actions, both with Iran Contra on behalf of Republicans, recent comments about the Mueller probe in general, and being put in his seat recently by Trump himself. So to file the letter without consulting Mueller doesn't help any of his credibility as we're left with a summary letter from a guy with no credibility and no sourcing documents available to see how he got to that conclusion.
Basically he doesn't need to but not doing so doesn't lend him any credibility when he needs it. Without the report, we don't know if it's bullshit, small spin, or accurate.