Hi,
See here.
The automatic upgrade uninstalls the previous version of VMware Tools, installs the latest version that is available for your ESXi host.
For advanced options, see here.
It makes a difference if you have ten or thousand of virtual machines. Upgrade and revert back often has been in correlation to additional security considerations like an actual snapshot, culprits in combination with older virtual hardware versions + windows releases, installation freezes because of antivirus, etc.
To get an idea about this early SDDC + IaaS learning curve, see here or here.
With every virtual hardware version, new capabilities were implemented in VMware tools as well. Also,
