If your dependant has earned income, creating and submitting a tax return will increase his or her RRSP contribution room. Also, it lets you determine the amount of any credits, such as disability amount or education amount, that he or she can transfer to you.
You can transfer information from your dependant's return when you create your own tax return. That way, you don't have to enter information twice and it's easier to claim dependant credits.
How do I transfer my dependant's information into my return?
Why don't all my dependants appear on the list of dependants to import?