What's the point of postcodes?

So a few Christmases now, I've had post addressed to 4 The Glebe in Bath.  Actually it's in Hinton Charterhouse, but that's near enough to Bath that the postal address looks like this:

4 The Glebe

Hinton Charterhouse

BATH

BA2 7SB

I've stuck with capitalisation and formatting as given by the Royal Mail's web site. 

For comparison, my own address looks like this:

4 Glebe Road

BATH

BA2 1JB

Obviously the "Hinton Charterhouse" part might help to - and is at least in part intended to - resolve this kind of ambiguity. But people can sometimes get addresses wrong, and sometimes just miss bits out, and the system should be designed to cope with failures and errors on the parts of human users. 

So the remaining part - the postcode - is the additional piece of information that might help. But no! The visual ambiguity there - possibly on purpose, for comedy purposes - isn't enough to resolve the issue: after all, a 7 and a 1 look similar, and only your local font will decide whether they look similar right now. Similarly an S and a J, and more so in handwriting that with machine print. (Maybe that's why I've only noticed this on Christmas cards ...)

So a cursory glance, I suggest, might easily yield "Glebe, BA2, 7SB" and "Glebe, BA2, 1JB" as the relevant pieces of information in the address. 

And so I get other people's post at Christmas. 

So ... The question is this: what is the point of postcodes?