AWS - semaphore signalling

[PJW]

Why is AWS provided only on the approach to distant signals in case of semaphore signalling?

Because the whole function of AWS is to act as a back-up to the visual indication gibven by the distant signal. This is the ONLY signal under semaphore signalling at which braking should commence. A signalbox may have many stop signals (homes and starters) along the line within the signalbox's area of control, but unless ALL of them are cleared then the distant must be maintained at caution and the train expecting to stop at the first stop signal; however if this can be cleared then the signaller will clear it once the train has been brought under control and nearly at it, then it would be dropped down to the next signal similarly until the one that can't be cleared.

The question should perhaps be "what is the purpose of fitting AWS to Red/Green signals under colour light signalling?".
I suppose the answer to that is; no real functional reason, mainly because drivers get used to having AWS at all colour lights and it might not be immediately obvious why one were "missing" just because the signal concerned was never a "distant" at which braking to stop at another signal needs to commence.