How essential is an isolation transformer?

[Refugee]

The isolation transformer I have is a 1000VA boat anchor and is seriously heavy and was designed to be bolted to a wall with conduit holes in the case. It stays under the bench and up at worktop height is a 1000VA Variac that remains plugged into the transformer all the time. I have a second pair of units that can be connected together consisting of a 250VA isolating transformer and Variac with 13A plugs and sockets on them. That big set up is staying as a fixed installation.
I got all the bits for free at various times over many years.