The general purpose for re-mortgaging your property is to either move onto a better interest rate deal or to borrow more money. Here are some of the more particular reasons why the majority of people decide to remortgage.
1) Raising Capital. You might consider remortgaging to raise money for things like home improvements or maybe you are looking to invest your money somewhere else.
2) Move to a better rate. Each lender offers different products and when the majority of product rates come to an end, you will typically revert back to your lender's Standard Variable Rate. Moving to another lender or different type of mortgage could save you money. Remember, it could be that the value of your home has increased meaning that you have more equity in your home and as a result means you could get a better deal.
3) Switch to a capital repayment mortgage. Your situation may have changed, and it may be that an interest-only mortgage or capital repayment mortgage becomes more suited to your circumstances.