These policies were very common in the past, such as the Irish Life Lifesaver Plan. Usually they are a regular monthly savings plan with life assurance attached. For example, you save €500 a month into the policy, and €50 is used as a life assurance premium with the remaining €450 invested in a managed or with profit fund . As it is a reviewable Whole of Life plan, the €50 life assurance portion is reviewed regularly and always goes up! After a long period in the policy, the life assurance premium could be more than the monthly premium (ie more than the €500 per month) so the capital lump sum value starts to reduce as they collect the shortfall.
I always recommend separating life assurance and savings, which is a much more common practice now. In many cases it is worth taking the 'encashment value' and investing in a better value stand alone investment, and then taking out a separate life assurance policy.
This would require some alanysis though to ensure it makes financial sense in your case, as there could be encashment penalties, and a new life assurance application with all the health questions etc can cause issues in some cases.