Your room temps are certainly fluctuating ... even though a household thermostat may read a constant temp at a certain spot, houses develop plenty of cool spots as you get closer to exterior walls, windows, and doors.
Human heating pads aren't made for supply a constant high temperature 24x7 and are subject to fault.
With a UTH that is designed to run at constant high and low temps 24x7 and a thermostat, any fluctations in surrounding room temps are taken care of.
I have several hundred enclosures all on UTH's and the temps are kept at exactly what I need them at 24 hours a day.
Hope this helps.
-adam