Carpet adds warmth and instant comfort to a space and is available in various piles and weaves. However, it is susceptible to water damage, mold [1], and mildew (not for use below grade); dust and dirt can break down fibers in the absence of regular cleaning. Carpets also provide safe harbor for allergens like dust mites [2] and mold.
Links:
[1] http://www.moneypit.com/audio-q-a/prevent-mold-under-wet-carpet
[2] http://www.moneypit.com/article/dust-mite-control-tips-and-solutions