I have many VM's that I never install VMware Tools in, it just depends on my needs. So, you can do it now or later... or never, whatever suites your needs/wants. 
From page 5 in Installing and Configuring VMware Tools.
VMware Tools is a suite of utilities that you install in the operating system of a virtual machine. VMware Tools enhances the performance of a virtual machine and makes possible many of the ease-of-use features in VMware products. For example, the following features are just some of the features that are available only if VMware Tools is installed:
- Significantly faster graphics performance and Windows Aero on operating systems that support Aero
- Copying and pasting text, graphics, and files between the virtual machine and the host or client desktop
- Improved mouse performance
- Synchronization of the clock in the virtual machine with the clock on the host or client desktop
- Scripting that helps automate guest operating system operations
Not all features are supported on all guest operating systems or in all VMware products.