what kind of impacts we can face if vmware tools are out of date.
The main one - performance issue for virtual machine as drivers may not update properly
VMware Tools generally works across different version, there isnt any material performance impact but general best practise is to have it same version as the hypervisor. Also, VMware Tools are backward compatible, so you can install the latest version from Index of /45848/tools
which performance issue?
It's always good to look at the release notes to see what fixes are done. Sometimes you see things and think.....mmm I have seen that before.
Last time...we had a few machines with a leaky vShield driver..which caused some DC's to crash. This got patched in the next version.
Too bad it can also be the other way around, maybe you don't have any problems and you introduce a new bug with newer tools version. You're never sure.
From my experience we apply the new VMware tools as soon as we upgraded the ESXi hosts. It can take a few months to get everything patched but so far we didn't encounter much issues with running 1-2 versions behind and the last level.