ink only or added watercolor?

I’ve been playing around with using a pale gray ink in a Kuretake brush pen for adding shadows to an ink sketch by adding De Atramentis thinner to De Atramentis Document black ink. This would save time over mixing a bit of ink and water on a palette. Most attempts were still way too dark.

But by adding just a smidgen of the thinned ink to a sample vial, then filling the space left with thinner, I finally got it light enough! It can be brushed on as-is or, for larger spaces, brushed on a pre-wettened surface.

Now’s there’s  a new quandary when sketching: do I leave a drawing “ink only” or do I add a bit of watercolor wash on top?