It's very useful to break tasks down so instead of a month long "upgrade elasticsearch" story, there's dozens of day-or-less tasks to work on. Often it's not noticed how much effort goes in to creating these new smaller tasks. If you aren't extremely familiar with the targeted version of elasticsearch, you'll have to spend significant amounts of time investigating, planning, and writing.

You can get very high accuracy on estimates by spending lots of time creating smaller stories and encouraging people to over estimate. This may not be in the best interest of the project or the business.