I think it applies more to the case where the variegation is unstable or cyclic, not regular variegation patterns like green centre, yellow margins on every leaf.
Where the variegation phases or cycles, some parts of one shoot, and different leaves, will be more or less heavily variegated.
In those cases it may be better to choose greener buds, which can become more variegated shoots later.
Highly variegated parts may not get back to being more green later on, and lack growth ability.
I have also found various variegated sports over the years, but most simply gave up or got taken over by regular new shoots from below.
Probably I would hedge my bets and multi bud each rootstock with variegated buds.