Version 10.12.6 is the and the final build of Sierra. If you download a raw Sierra installer (e.g., 10.12.0), you will immediately be forced to update to 10.12.6 via the App Store anyway. By downloading the combo updater or the final installer, you save hours of patching.
Feasibility and Procedures for Acquiring macOS Sierra 10.12.6 Date: Current Date Subject: Analysis of download options for legacy OS version 10.12.6 work download macos sierra 1012 6