I was about to install a dimmer switch module (MK K4501 BSS BLV) to
control a group of 4 low voltage halogen downlighters that are each
supplied via their own individual ( 220 volt a/c to 12 volt DC)
transformer.

But, the installation instructions says that the dimmer should not be
used in a circuit with more than 3 transformers.

Can someone, who knows about electricity theory please explain the
reasons behind this limitation. And, if more than 3 were connected,
what would happen?

VT