Did you recently have a home inspector or a chimney service professional tell you your chimney was in need of a new liner? 99% of time this is due to a safety concern. 1% of the time it's too improve the efficiency of your wood stove or fireplace, which is a great side benefit of having a stainless steel chimney liner installed.
Masonry chimneys were built to withstand years of abuse from the elements. Fire, wind, and water of all sorts are exposed to your chimney internally and externally. Over the years, the clay flues that currently reside inside your chimney and serve as venting for your wood stove or fireplace become cracked and deteriorated, in some cases far worse than others.
It's important to keep in mind that even the tiniest of cracks in your clay chimney flue are a cause for concern because carbon monoxide gasses could potential be leaked into your home putting you and your entire family at risk.