There is no trade-off: In the UK, postcodes are much more specific, and there's always manual address entry.

Unless ‘manual address entry’ implies that the postcode is not a necessary part of an address, then there is the trade-off that postcodes in the UK are (basically) recipient-specific, whereas postcodes in Germany are town-specific. If I know my parents’ postcode, I know the postcode of someone living three streets away from them and hence only have to remember the street name and house number, whereas I need to remember the postcode of that particular recipient to address a letter in the UK.

However, as I said, such data being easily available nowadays renders this point somewhat moot.

I don't understand. Why are you mentioning the trade-offs of doing this in Germany when I'm talking about the UK?

Even so, postcodes in the UK aren't town-specific, they're more like street-specific, roughly.

I am comparing very specific postcodes (as in the UK) to very broad postcodes (as in Germany). While the former allow for very simple addresses (street number + post code), they come with the trade-off I mentioned.