Monitoring temperatures if you use heat pads is quite frankly a life or death situation in many respects for our snakes. In most situation we don't worry too much about lower temps. as our homes/apts. are usually within a range that suits our snakes.
It's the high temps. that can be the killers. Trusting a uncontrolled heat mat is a roll of the dice. In most situation they don't create the kind of heat that is dangerous but if it happens snakes could be lost.
I feel the bare minimum you should be doing is monitoring your heat mat temp. with a digital temperature gauge. These gauges are relatively inexpensive and allow you to view the current temp. your mat is producing. Diligently watching this gauge will let you head-off any dangerous spikes in temperatures.
Using a thermostat serves two purposes as it monitors the temp and adjusts it to you specification not allowing it to spike.
There are many thermostats available in the market today, some not very expensive and other high dollar. Some do the basic job of temp. control and others will control not only temp. but also light cycles and humidity.
I have posted links to some of the thermostats that are available and a digital temperature gauge I use.

Amazon.com: Zoo Med Digital Terrarium Thermometer: Pet Supplies

Here is a link to some of the other companies and their thermostats.

Ranco ETC-111000 Pre Wired - Reptile Basics Inc

Temperature Control - Herpstat Proportional - The Bean Farm

Vivarium Electronics VE-100 - Reptile Basics Inc

Digital Temperature Controller for Heat Mat