VMware Tools is a set of utilities installed on the guest OS that improves the overall performance and gives better control of the VM, making administration easier. VMware Tools is not installed by default.

Although, a guest OS can run without VMware Tools, the management of power controls and other features is not available until you install VMware Tools. Shutdown or restart options, for example, are not available without VMware Tools. An improved graphic interface, a better mouse control, and the ability to copy and paste files are some of main benefits you notice at first sight after the installation.

VMware Tools delivered with vSphere 6.5 introduces some enhancements that improve the manageability experience:

• Signed ISO images: VMware Tools is distributed as ISO images to be mounted to individual VMs to install or upgrade. To increase security, in ESXi 6.5, the ISO images are cryptographically verified each time they are read. Additional files with appropriate signatures have been included in the VMware Tools distributions to help this verification.
• Bifurcation of VMware Tools for legacy and current guests: vSphere 6.5 delivers two versions of VMware Tools, 10.1 and 10.0.12 described as follows:
  • Version 10.1 is available for OEM-supported guest OS only
  • Version 10.0.12 is offered as frozen VMware Tools that won't receive further enhancements for guests no longer supported by their vendors
• Bundling of tools for most popular guests only: ESXi 6.5 includes VMware Tools for the most widely used guest OS but VMware also provides  tools for other guests (see download at https://my.vmware.com/web/vmware).

For more information on VMware Tools, see the blog post at https://blogs.vmware.com/vsphere/2017/11/every-vsphere-admin-must-know-vmware-tools.html. 

A recommended practice is to upgrade to the latest VMware Tools version included in your ESXi. VMware vSphere 6.5 Update 1 includes VMware Tools version 10.1.7.