Here's the scenario – you are a songwriter, possibly a performer too. You're in the studio with a top producer. The producer is helping you work on the song some more before starting to record, because he doesn't feel that it is quite working properly yet.
This is a common scenario, and in fact it is an important part of the producer's role to encourage the artist to better standards.
However there is a fine dividing line between encouragement and actually contributing to the song. A producer may suggest a word here or there; perhaps a subtle change in the melodic line. It all helps.
But the when the recording is finished and well on the way to release, your management gets a call from the producer's management (or worse still, their lawyers) saying that the producer now wants a half-share of the writer's credit for the song.
And that means a half share of the royalties.
Potentially this could add up to a significant amount of money, particularly if the song is released as a single.
The producer would argue (or at least his management would) that without his help, the song would not stand a chance of success. The artist would argue that the producer was simply fulfilling his role and he is already being paid for that work.
It does often happen that a producer genuinely does co-write a song, in which case they do deserve a credit, and royalties. Producers are often songwriters themselves. (Sometimes the reverse is true and the producer has written all of the songs, then the artist claims that his ad-libs deserve a writer's credit).
As a newcomer to the industry you would almost expect to be taken advantage of in this way. And since you're the small guy compared to the established industry reputation of the producer, there's not much you can do but take it on the chin.
When you are more established, then you will have the status to resist this kind of manipulation.
And if you are a truly great artist, then you will welcome contributions to your work. You will make it your business to make sure that people who help you are rewarded fairly and fully!