I might not re-mortgage in order to raise capital to invest, but if the interest rate is low (i.e. not right now) why would you put up more of a deposit than yo

I might not re-mortgage in order to raise capital to invest, but if the interest rate is low (i.e. not right now) why would you put up more of a deposit than you have to? It's a cheap loan for however many years, and if it rises you can just put up more then, having benefited in the meantime.