It isn't clear from this (thanks BBC) of what impact this will have at UK airports? Or is this just something for sea/Chunnel crossings.
On the contrary, the article makes it pretty clear that the existing APIS fulfils the same function for air passengers.
Combat illegal immigration by checking those on the way out? Seems reasonable
Yes it does. There is currently no effective way of checking that someone on a tourist or educational visa has left the country by the required date and isn't remaining in the country illegally. Hence passport exit checks.