Imagine you have a web startup and as soon as people visiting your website start coming with reasonably large data sets, your website becomes noticeably sluggish.

And then a competitor pops up and they are dealing with the same sized data blazingly fast, instantly from the user's perspective.

And you look into it and they are using the same technology stack you are using.

It's at that point that you might start to care about the difference between a linked list and a hash table.