Their virtual warehouses usually take only a few seconds to spin up, but can take longer (especially for large warehouses).

If you keep the warehouse running, there's a fair amount of caching going on behind the scenes that can make your queries run faster on the warm warehouse (how much faster depends on the query) . This article shows one example - a cold query ran in 20 seconds, after caching it ran in 1.2 seconds on a warm warehouse:

https://community.snowflake.com/s/article/Caching-in-the-Sno...

So you don't always want to set the idle shutoff time to the minimum.

There are probably other use cases, but I only think of data warehouses for supporting batch/analytical workloads where latency is not a problem because the entire job takes minutes/hours to complete. In which case cold start does not significant.

Analysts and other data consumers don't want to wait 30 seconds for cache warming every time they refresh their dashboard.

Also, since you're paying by the second, it can be cheaper to keep a warehouse running longer to avoid having to re-warm the cache with every query.