Monitoring a cluster for memory and compute usage is an integral part of an administrator job to make sure the cluster is healthy and stable.
You could face a situation in which you just went through an ESXi upgrade and now noticing that CVM Memory is displayed as 100% in Prism UI and VMware Web Client.
Is my CVM really consuming 100% memory and do I need to troubleshoot further regarding where the memory is getting utilised?
There are chances that this might just be a cosmetic issue, happened after an ESXi upgrade due to how active memory heuristics works and active sampling happens in an ESXi environment.
The following Knowledge-Base article will help you to understand the issue better thus helping you to isolate it to your environment.