ZZ plants have tuberous roots (potatoes are tubers) that need a lot of space and the more airy the soil, the less risk there is that they will rot.
https://upload.wikimedia.org/wikipedia/commons/6/62/ZZ_Plant_%28Zamioculcas_zamiifolia%29_roots.jpg
Someday I hope the myth of "this plant likes to be rootbound" or "tight shoes" or whatever the phrasing, will die. No plant likes to be rootbound. What is necessary for plants to stay
alive is for their roots to not rot, which can happen so easily in a pot
with dense soils, like ground dirt, or bagged mixes of predominantly
tiny particles of peat, (or to simply shrivel from simply never getting
any water.) Having very little soil around the roots would make the soil
dry more quickly, and for even the most dedicated plant-overwaterers to
not rot the roots of their plants. This is not ideal, since most
non-cactus plants are stressed by dry conditions, it's just a way of
coping with soil that has little air in it when moist.
Negative experiences in regard to potting-up, where an undisturbed root
ball is placed into a bigger pot with more soil around it, vs. doing a
repotting, as described below, can give rise to old wives' tales about
plants not liking to be repotted/disturbed. Potting-up a root-bound
plant that has roots surrounding the outside root ball often lead to
this negative experience because those roots had adapted to accessing
oxygen around the outside of the root ball and surrounding them with
more dense, soggy-but-airless potting soil will likely lead to
suffocation.
The reason bonsai masters are able to keep potted entities alive for
hundreds of years is because they care for the roots by trimming them
and changing the soil. A plant grows from the roots-up, so if the roots
are not healthy, gorgeous foliage will decline &/or no flowers can
form. When you unpot a plant and find a pancake of roots at the bottom,
chopping that off will give roots a chance to grow normally again for a
while and will make removing the old soil easier.
Roots need oxygen & moisture at the same time to function. Just air =
shriveling. Just moisture = suffocation & rotting. Either will
cause root death and dessicated foliage because the roots have been
unable to deliver moisture. Having to let soil dry, as if ones' tropical
jungle plant was a cactus, is an unnecessarily stressful coping
mechanism for non-desert dwelling plants in soil without enough oxygen
for the roots to stay healthy when it is moist and can lead to premature
loss of older leaves and in extreme cases, dry shriveled roots/dead
plant.
The ability of roots to be able to function properly depends greatly on
the soil structure/texture, which can change over time. Potting soil
tends to be very dense, mostly peat, with very little air in it. Any
kind of organic ingredients decompose into smaller bits over time, and
roots fill air spaces over time as they grow through soil. Replacing
soil periodically is usually necessary to keep plants healthy because of
these reasons. A more porous, chunky, airy soil (like cactus/palm, if
one is buying bagged,) can have more air in it even when it is moist
because there is space between the particles. When there are tiny
particles of any kind in a pot, such as peat, sand, silt, clay, they
filter into all of the tiny spaces in a pot, eliminating the air.
"Overwatering" is the label and manifestation when roots have suffocated
and/or rotted, combo of both. Over time, organic bits decompose into
smaller bits, so even the "best" soil, if it has organic components,
will need to be replaced when this happens. The speed at which this
happens depends on many variables, but on average, about 1-3 years.
Q
Remember this for life!
Q