The high value, but 'difficult to describe until you've experienced it difference' I've found is the smaller cabin of more seasoned flyers. That makes a big difference to the flying experience -

The service extras can be nice, and the extra recline and space (2x4x2 at worse) do add up on longer flights.

But it depends on the value. When it's only a tiny bit more than WT... AND the gap to CW is large, it makes a lot of sense.

Finally, it can be a very efficient means of piling on the tier points. WTP flights earn 90 at least, which can be a big jump from the 20 on the lowest WT fares. That's "almost CW" levels in comparison. Especially if combined with a good BA holidays fare......