Does challenge's help us .... because questions are repetitive!!

Answer 1

They can only be helpful at the beginning. When you're used to it. You would see that the questions are all the same and you rarely get a new question.

Answer 2

Challenges are mainly for fun, however, they can be helpful too.
They require you to use programming basics in order to solve them, thus, using the same skills over and over again will establish these skills in your mind.