Cache is something to consider in order to reduce loading times of webpages on your site that have excessive images or assets increasing that pages file size. This can especially be useful if a webpage has flash, custom scripts, or other things of that nature.
Google maintain information about your site, it is important because Google frequently (every second) update there SERP, and it depends on what types of changes you brings in your site both on-page and off-page, so caching always affect your site in SERP.
The importance of cache is, it is extremely fast memory which is used to store instruction and rapidly used by the CPU.It accelerate CPU instruction retrieval process.