When is it best to sanitize user input?

Question

User equals untrustworthy. Never trust untrustworthy user\'s input. I get that. However, I am wondering when the best time to sanitize input is. For example, do you blindly

Answer 1

I find that cleaning it immediately has two advantages. One, you can validate against it and provide feedback to the user. Two, you do not have to worry about consuming the data in other places.