Heating mats are convenient forms of increasing the temperature, if your grow area needs it. As opposed the conventional heater, mats distribute heat evenly, gently warming your cannabis plants from the bottom.
Though it might be used wherever a reliable source of heat is necessary - in cold attics, basements or abandoned factories, or to gently warm the hydroponics nutrient vat - it is especially recommended for handling of seedlings and clones. The sizes of available heating mats are usually corresponding to the most popular propagators - some are even integrated with one, and constitute a part of most advanced germinating kits.
Heating cables fulfil the same role, of providing heating from the bottom, where even distribution is important (i.e. almost always in cannabis cultivation). These are available with build in thermostats, allowing for temperature to be controlled automatically, adjusting to the changing conditions inside the grow area.