I always thought that a minimized client consums just a very small amount of data, which is required to keep the connection up.
But now I found out, that the current version shows a strange behavior when the client window gets minimized.
Please see the following bandwith monitoring screen when the client is normaly opened and when it is minimized.

It draws more data when the client is minimized as when it is normaly opened.
I use the client version 1.2.0.1 with the following connection options:

The server runs also with version 1.2.0.1.
Server admin properties:

Server properties:

I think the behavior of earlier versions was there different.
I also have tried to connect a UltraVNC client to a TightVNC server and there the data consumption when the client is minimzed is fine.

The bandwith usage with an opened viewer window (UltraVNC) is in general much better connected with a TightVNC server than with the UltrVNC server.
I used at all tests the client connection options which I showed before.
UltraVNC server, screen is opened and is refreshing

TightVNC server, screen is opened and is refreshing

That all means to me that the problem is on the server and not on the client side.
Greetings
Michael