I’d say it’s a choice. Twice I’ve used vacation mode (one for weddding week when family flew in, the other for honeymoon). Twice this decision really kicked me in the teeth.
Getting back into it was a bit of a demotivating struggle both times. The lack of review pressure also kept me away from WK for almost a month the second time. That was a big mistake on my part.
But! At the same time: you couldn’t have paid me to give a bleep about my reviews or SRS while on my honeymoon. I had no intention of spending time on the regular, daily grind in such a situation.
So I say: if doing your reviews would have a negative impact on an amazing vacation: holiday mode. Screw it. You should enjoy and indulge in your one life sometimes, too.
If you’re using it, I’d suggest to steel yourself against the thought of a rough re-entry. Don’t get demotivated if your level-up time or accuracy slips for a while. It will get back to your old norm. Don’t give up.
TL;DR: While using vacation mode has booted me in the rear before, there are things that warrant a mild delay in the kanji study.