Many old houses have been repointed with cement over the last century and a half. Because cement is harder than the surrounding brick and stone and does not breathe, water will become trapped. When the water crystallises with the first frosts, the stone and brick will tend to spall, and timbers rot.
If the cement is replaced with lime, this softer pointing will act as a wick, drawing water away from the structure of the building and leaving it sound and dry. It is also a very great deal easier on the eye.