I look at it as to 'the interpretation' of the particular director/actor/actress. It's all up to them, as to how they wish to deliver a line:
LES MISERABLES is a pop-opera (SUNG-THROUGH)
* However, I know a few singing actors who have done several verses speaking a few lines here and there. *
VALJEAN: "We meet again..."
JAVERT: "You've waited for this all your life.
Take your revenge,
How right you should kill with a knife."
VALJEAN: "You talk too much,
Your life is safe in my hands..."
<-- That sequence is known to work both in-song and spoken word ... YouTube it for reference. I know I'm not alone in this.
SWEENEY TODD is an all-out operetta.
JEKYLL & HYDE (operetta)
THE WOMAN IN WHITE (operetta)
PHANTOM of the OPERA (operetta)
A LOT (if not ALL) Sondheims are heavily, heavily dependent upon the songs to tell the story, or at least, have the audience take-in the goings-on (ie: COMPANY, SUNDAY..., etc.)
I'm not sure about CAROLINE or CHANGE though.
Having never seen it. Unfortunately.
Best,
- Mike