Sute-In is to be stamped to accept the other one can correct wrong place without permission if he realizes a mistake on a contract. Sute-In is your intention to accept comprehensively that your contractor changes a content written in a document. Ste-In needs to be stamped in a blank space of a contract.
If you are a contractee, stamping Sute-In on a contract allows your contracter to re-write a content freely. So you must be very careful to stamp this seal. However, the situation where you are required to stamp Sute-In mostly applies for the case that you make a contract that has possibility to need a strict correction by difference of the formality of a contractual document. If your contractor is trustful enough and you have a document that requires you to write and correct with strict formality, Sute-In helps you to ask contractor to handle it rapidly.
But the most important thing that you need to do is to always judge whether or not you stamp it on each occasion that you come across this case.