To start this topic, it is worth to mention the difference between the data size units. There are GBs (gigabytes) and GiBs (gibibytes). The difference is the following:

GB = 1000 MB

GiB = 1024 MiB

So, the difference is in binary vs decimal representation. It can be confusing, because a lot of people have never heard of gibibytes and always thought that GB is 1024 MB. In fact, it is not exactly true 

Why it may be confusing in Nutanix running on ESXi hypervisor?

Nutanix is using MiB, GiB, TiB, etc as data size units. When you create a storage container, you get the size in binary units. For the example, i have created 2 containers with advertised capacity of 1000 GiB and 1024GiB:

We can see, that the 1000 GiB container is 0.98 TiB is total size, because 1 TiB=1024 GiB.

However, when we go to the vCenter, we can see a different picture:

vCenter reports that the 1000 GiB container is 1000 GB in size and 1024 GiB container is 1TB. But 1 TB is 1000 GB! The problem here is that the vCenter shows tebibytes (TiB) and gibibytes (GiB) as terabytes (TB) and gigabytes (GB), which is wrong. Since vCenter is the product of VMware, Nutanix cannot do anything about it. I believe VMware made it for simplicity and to avoid confusion with the units that people are not used with. But that can cause a slight difference in numbers between the Prism and vCenter. The fact is that the TB and GB in vCenter are actually TiB and GiB and there is no lost storage space there, the whole container size can be used.