A while back ago CDNs would market on their TTFB - that is the 'time to first byte'. It sounds like a really important number and the lower you can make it the more impressive it looks. At the end of the day though it doesn't really matter cause a single image can be tens of kilobytes or even megabytes in size. A single page can have 80 some odd requests and transfer multiple megabytes in resources. So while it is interesting it's a bit of a vanity metric. Boot time is one of those vanity metric...