When you are trying to tell someone a story, your ability to come across as credible heavily depends on the number of details that you can offer. The more details, the more credible the story seems. 

Let us take two arguments from a court case:

The mother took great care of the child and also ensured that he brushed his teeth before going to bed.

The mother took great care of the child and also ensured that he brushed his teeth with his Darth Vader toothbrush before going to bed.

The second statement makes it seem like the mother is far more involved and concerned about the child than the first. 

Details provide a degree of credibility that cannot even be brought by an expert. If you are looking to convince someone, whether it is because you are fighting a court case or just marketing a product - add details.

The more details you add, the more legitimate you seem.

Reversal:

When telling a story, it is important that it is non-falsifiable. 

Often time stories fall apart because there seem to be timeline issues or the details do not match. That can really result in the downfall of a story. 

So while details do add credibility. If done without much thought, those details can end up contradicting one another quite easily.