As it is performed prior to a property being found and chosen, it does not take into account the particulars of a specific property and valuation, which is why uncertainties can arise. Pre-approval are helpful for those who want to know how much they can borrow before attending open homes, and can be reassuring for new borrowers, the real estate agent (when signing a contract) and the seller of the property. When someone gets a pre-approval, they can start looking at properties knowing how much they can borrow. They know what their price range is and you can take comfort in knowing that a lender has looked at your application to make sure it meets policy.
Pre-approvals are usually valid for up to 90 days but, depending on the lender, may be renewed to allow more time to find a property.