By combining 矮 (ǎi - short) and 小 (xiǎo - small), the word 矮小 creates a more specific and vivid image than either character alone. It emphasizes a lack of both height and overall size.
In Chinese culture, as in many others, there can be a social preference for height, particularly for men. Being tall (高大, gāodà) is often associated with strength, reliability, and good prospects. Consequently, describing someone as 矮小 can carry a subtle, and sometimes not-so-subtle, negative connotation. It's a factual description, but it highlights a physical trait that is not typically considered ideal. A useful comparison in Western culture is the difference between “short,” “petite,” and “stunted.”
Therefore, while 矮小 is a common descriptive word, one should be cautious when applying it to people directly, as it can be perceived as insensitive. It is much safer to use when describing plants, animals, or inanimate objects.