In a defining relative clause, you use the simple present tense, not "will", when you are clearly referring to the future in the main clause.
Any decision that you make will need her approval.
Give my love to any friends you meet.
The next woman I marry is not going to be so damned smart.
However, you use "will" in the relative clause when you need to make it clear that you are referring to the future, or when the relative clause refers to an even later time.
Thousands of dollars can be spent on something that will be worn for only a few minutes.
The only people who will be killed are those who have knowledge which is dangerous to our cause.
I sent my boys to a good public school so that they will meet peope who will be useful to them later on.
Student or Learner