In a nutshell, you should include a review section whenever you are making a recommendation in respect to a client's existing plan or investment. This could be a recommendation to encash, transfer, rebalance, re-register or switch the underlying investments, amongst others.
To ensure you fulfil the regulator's expectations of you in respect to Replacement Business, you must include the relevant review section if you're recommending the transfer, encashment, surrender or drawing of benefits from an existing plan. This is typically associated with pension switching, ISA transfers, protection rebrokes and investment surrender and reinvestment cases.
Within a review section you will be prompted to include policy details for the existing plan, confirm the reasons for your recommendation; and (when necessary i.e. if it's replacement business) compare the charges, investment performance and the benefits and features of the existing product and the proposed alternative. These are all required of a compliant suitability report.