One of the unforeseen problems that occur in bare bottom tanks, is that a large proportion of your beneficial bacteria will only be sequestered in you filter(s), and if power goes out for any length of time, or....your filter bites the dust, or even simply becomes plugged,
the tanks bio activity may be curtailed enough to become problematic.
In a tank with substrate, ....that substrate is home to a large proportion of beneficial activity, and may buy you a little leeway until you can get the problem is rectified.