Pretty self-explanatory, it's unnecessary for the party to do an elaborate hoe-down every time I want to cast Guidance on my party lead. Particularly through acid puddles, raging infernos and the like. Just a little toggle by the party portraits that will freeze any characters I'm not explicitly moving until its un-toggled. Would be a HUGE quality of life improvement.

Like many, my #1 request is to remove the chained/unchanged portraits system (auto-follow) and replace it by the good old, universally approved, simple system of "Select character(s) 1 | 2 |3 | 4 | Pet A | Pet B" or "Select all" to move those characters/creatures. Usually games offer a hotkey to select all if what we want is for every character to move together.

In the case you mention (OP), selecting your caster should have only her/him move and cast. Simple enough.

The old system, which I endured all of DoS1, should rest.

Larian has not responded to this popular / common sense request.