Bathtub liners are quite expensive. Average price in Toronto and GTA is about $2300 for installation.
Water can get between the liner and bathtub. It can cause a leak and mold to grow. Also it is not safe to use a bathtub when its bottom moves under your feet.
Any problems of the bathtub would not be fixed. Liner just covers the surface of your bathtub. Any of these problems can get worse over time.
This service is limited with a size and shape of the bathtub. In most cases acrylic, fiberglass, and free standing tubs can’t be lined. Also there is always a 1/2 -1 inch gap between the existing bathtub and liner. Moisture and humidity can cause mold and other unpleasantries to grow in this gap without anyone knowing.
This bathtub liner was installed by previous owner of the house .There was no information about the time it was installed. The new owner of the house has been using the bathtub for quite a long time with no problem until he noticed that the bottom of the bathtub became a "water bed". Liner was removed and bathtub was refinished with spray enameling.