Why remortgage?
The primary reason is saving money. A mortgage for most people, is the largest financial commitment of their life and as such should be scrutinised regularly to ensure you are paying as little as possible for your borrowings.
A changes in circumstances is another good reason to look at remortgaging. Imagine, for example you change your job and go from a steady monthly wage to consultancy work, your income is not necessarily monthly any more. Whilst a fixed rate monthly payment mortgage may have lower rates, your wage is not necessarily monthly anymore. As such a flexible product might be more sensible choice, allowing you to take payment holiday on month and an overpayment the next without charge.