Most caveat loans use a registered caveat for speed then convert to a 2nd mortgage. As such, they are allowing the lender the authority to sell your property in the event of a default.
Getting approval from the First Mortgagee to register a 2nd mortgage can take time. Consequently, you can reduce settlement speed by using a caveat. Therefore, you have access to funding while the lender lodges the second mortgage.
In summary, a registered caveat allows access to funding fast (24-72 hours).