This is a good question - your adviser will do a transfer value analysis TVA which will produce a report showing many different calculations
One of the calculations show you the cost of securing the pension by purchasing an annuity. For example if you at retirement and the transfer value is £100K but it will cost £ 125K to buy an annuity you will know it is 25% more expensive to replace the pension income in your own personal pension
Another calculation is how long your money will last if you take the pension as drawdown
Apart from these hard facts there are soft facts e.g. importance of flexibility and ability to leave money to the family that need to be taken into account
