I don’t understand why the pronoun “le” is added to sentences where it doesn’t seem necessary.

https://www.lawlessfrench.com/grammar/definite-article/

Another example not covered in the lesson on definite articles:” Oui, je l’ai dit” meaning “Yes, I told him”. It doesn’t mean Yes I told him it, so why is the “le” or “l’ needed?

Maybe my answer to your similar question above sheds some light on this?

When learnining French, I often banged my head against the wall when asking "why is that..." questions. Often the answer is simply: because that's the French way.

That said, in sentences of the type you refer to, a previously mentioned idea is implied. "I told him." is only meaningful if the speaker knows what he told him. In English, you can leave that implication hanging in mid air and all's good. Not so in French. Here you need to tie that implication to the pronoun le.

The problem only arises when, in your head, you're translating the French (with the le) to English, where it sounds superflous. My advice is just to stop translating.

Judy, 

effectively ' je l'ai dit ' does mean " I told him it (that/something) " as Chris highlights, but that is simply not what we would usually say in English. 

It is important to remember that  " translation ",  is not the same as word for word ' rewriting '.  

You might also find the attached link useful : 

https://www.lawlessfrench.com/grammar/neuter-object-pronoun/