delta76 Doram unless if you have a very very fixed schedule, you will find yourself in situations when you need to wait for a good espresso. And in many cases if your machine heats up in 15 minutes, you can make some latte to go in 20 and leave happily. Or your machine needs 25 minutes and you leave angrily and have a dilemma of whether you get a Starbucks instead.
Not anyone needs a fast warm up machine but if everything else equals, fast warm up time is a pretty big plus.
Note that I didn’t say warmup times are not important, but rather asked how far would we obsess about it, and at what price.
If two machines are otherwise similar and one warms up in half the time, then of course it’s a bonus for many. But if you want to shave 10 minutes from a 24 minute warmup - what is it worth to you? Different people will have a different answer to that question, and that’s normal of course.
As for leaving angrily to a Starbucks - you could do that, or - as I suspect many people with non-instant espresso machines do - you can get used to a routine that includes a bit more planning ahead (for instance, a person who has an instant-ready machine might not think about espresso while having lunch, and just remember it when he is ready for a coffee, but if the same person had a machine that took 24 minutes to heat up, and he usually wants a coffee after lunch, then he might get into a habit of turning the machine on when he starts his lunch, so it’s ready when he wants to use it).
Other parts of this hobby (and life, in general) require even longer term planning. For example, one might plan weeks ahead to make sure they have freshly roasted, well rested beans ready for their instant-ready machine. Or, they can angrily dash to Starbucks when they run out and realise that new beans aren’t available instantly. We also don’t expect our lunch to instantly land on our plate the moment we think about it, do we? It’s all relative. :)