The Capital Gains Tax (CGT) exemption is a valuable allowance. At £10,900 for 2013/14, it's worth £3,052 to higher rate taxpayers paying tax at 28% on their gains.
But it's a 'use it or lose it' allowance. It can't be carried forward.
There's a monetary argument for investors sitting on an investment portfolio with significant capital gains to realise enough each year to fully use their exemption. The proceeds can be reinvested, but the accrued capital gains within the portfolio will reduce. Read this post