Mulch is highly contentious. Read Steve Solomon's book "Gardening in Hard Times" (not 100% on the title) to look at his experiments on mulching. Basically, he says that if you have any exposed soil, mulching only brings more water to the surface, which contributes more to drought, whereas bare soil, once desiccated to a few inches, provides a barrier to the wicking process, which allows for far better water retention.
Having the situation I described isn't ideal (Steve is/(was?) a european style farmer trying to figure out adaptation to the pacific northwest area so his methods can be said to be cultural adaptations rather than horticultural solutions), but if you want to avoid it, I would guess that a living mulch provides much the same benefits, without creating a desiccation zone. Plants with small surface root zones, I suspect, would do the same as an 'airy' mulch.
Again, if the mulch has lots of contact with the soil, and if it is too consistent of a texture all the way up to the surface, wicking will bring water up from a great distance to be evaporated by the sun.
On the other hand, mulching for the purpose of creating shade (and reducing solar surface evaporation, makes a lot of sense to me - shading the soil allows for a relatively decent cover for all insects, both predator and prey (spiders centipedes and ground beetles need cover as much as everything else) so you haven't messed with whatever balance you have. I have considered the advantages of learning basic, haphazard methods of weaving in order to create shade "foils", which might allow for your 'shading mulch' to avoid contact with the ground, which would prevent it from immediately beginning to decay.
Mulching with certain materials like shredded interior tree wood might work simply because it doesn't break down fast enough, but has so many huge disadvantages (soil imbalances, ecological dead zones, high labour) that it does not seem a solution to me. Also, I find that such mulches are often applied in bad situations - deciduous trees, for instance, often (in my area) get mulched with coniferous 'bark mulch', which means that the soil bacterial/fungal content, typically carefully managed by the deciduous leaves themselves so as to benefit the tree, is replaced by what I can only imagine is something that only benefits conifers.