Subtitling live broadcasts makes them available to a larger audience at once. For example, in the case of briefings and special broadcasts, this is particularly important in situations where information needs to be shared quickly.
Subtitling programmes after the fact has been known about for decades. Subtitling live broadcasts, on the other hand, is an entirely different practice, as people clearly speak faster than a subtitler can write. A machine faster than humans will fortunately help to solve this problem.