A language like this one can be used to develop cryptography libraries like OpenSSL. If two documents have the same length, but differ in the time it takes to

A language like this one can be used to develop cryptography libraries like OpenSSL. If two documents have the same length, but differ in the time it takes to encrypt them, then their encryption times leak information about their contents. In cryptography, this is an example of a "side channel" - and side channels are considered bad. A "constant time" language helps minimise the presence of such side channels, making it useful in cryptography.