I have my heat only boiler in the loft. Hot water cylinder in the airing cupboard in the hall downstairs, pretty central to kitchen sink, ground floor WC and first floor bathroom. Hot water gets to all three in about ten seconds.
My mate has a combi boiler in his loft and it’s a good minutes wait until hot water reaches his kitchen sink. Of course he's wasting water waiting for hot to arrive and when he turns the tap off, there's a couple of sink fulls of hot water in the pipe that is wasted when it cools down. They either usually wash up in cold water or use the kettle. Pain in the arse with a combi in the loft when you need just a sink full of hot water in reasonable time downstairs.