It means that three weeks into your project your realize you fucked up when you required a full HTTP transaction for every log entry, however beautiful the API may have looked during the specification phase, that not even the really fast transactions-per-second web servers are fast enough, and already one week over your carefully crafted perfect time estimate you have to throw everything out and start over again.

Yeah, I'm not a big believer in accurate time estimates either. Routinely accurate time estimates imply that you're doing something wrong. If your work is routine enough that you can routinely accurately estimate it, you're missing an automation opportunity somewhere. Probably a big one.