Naomi Glass wrote:

We are considering a load of red lava rock as a mulch for
existing front lawn plantings and as a fill for areas to be targeted
for planting in stage 2 of our GET-RID-OF-THE-DISFUNCTIONAL-LAWN
campaign. Any pros and cons would be appreciated.

Naomi Glass
Kirkland, WA, where it's pretty dry out there...

As others have mentioned, lava rock adds nothing to the soil or to the
plants it surrounds, does little in the way to discourage weeds (pore
space between rocks is too large and seeds will germinate) and is very
messy to work with should you decide to change or add to your plantings
down the road. And if conserving our limited summer moisture is a
consideration, then a good, fluffy, organic mulch will offer far
superior results.

I commend your intent to reduce your lawn area - it's a huge drain on
resources and a water hog - we could all do with considerably less lawn.
But before you spread red (RED??) lava rock all over the place, you
might want to consider hiring a designer a or a design consultant to
help you come up with a more natural looking approach to a no-lawn
planting. There are a number of ways of going about this to achieve a
very natural and attractive low maintenance and low water use garden
more in keeping with our natural PNW sensibilities than a cover of
glaring red rock.

pam - gardengal