There is a reason Barr talked in his letter about having Mueller and Rosenstein assist in deciding what can be released. There is significant information in the report.
Mueller uncovered a great deal and indicted quite a few including Manafort, Flynn, Gates, Cohen, Stone and 13 Russians. There are more. see
All of Robert Mueller’s indictments and plea deals in the Russia investigation
And because of the investigation, we found out about the hush payments, and the ongoing negotiations for Trump Tower Moscow during his primary campaign, and much more. He may not be recommending indictments simply because there is not enough evidence for conviction despite the strong suggestion it took place.
Robert Mueller report will be a gold mine of improprieties. Trump shouldn't celebrate yet.
A Mueller decision to decline any new indictments does not, by itself, mean that Mueller concluded President Donald Trump committed no crimes. In only means that Mueller followed DOJ protocol that prohibits the department from indicting a sitting president.......
Profoundly 'swamp-like' conduct at the least
Given the evidence already breaking the seams of the public domain, it is hard to imagine that Mueller’s report will offer a full exoneration of the president and his campaign. Democrats may be disappointed that Mueller did not indict the likes of Donald Trump Jr. and Jared Kushner, who many consider the closest orbiting co-conspirators to the president. But, given the signs that Mueller’s investigation has been thorough, his report will likely be a treasure trove of evidence that, if not establishing outright crimes, will establish profoundly “swamp-like” conduct by Trump and members of his inner circle.
Perhaps the most significant question Mueller’s report can answer is whether there is evidence that Trump has been compromised by Russia. It may not be a crime to lie to the American public about currying favor with a foreign adversary, to make hundreds of millions of dollars by building Trump Tower Moscow. But it helps explain the president’s siding with Vladimir Putin over U.S. intelligence agencies and his refusal to implement
congressionally mandated sanctions against Russia for its election interference.
If Mueller’s report is the gold mine of impropriety I predict it to be, expect Barr to refuse full disclosure and the resulting battle to end up in the Supreme Court.
And investigations were handed off to others such as the Southern District of New York. see:
After Mueller: The Ongoing Investigations Surrounding Trump
We need to hear more about what is in the report.