What's the purpose of infrared handheld?

I realize that infrared wavelengths are used in the medical field and industry. I see really nice handhelds that are infrared and people buy them. But I can't understand why. I mean they don't really do all the "handheld" things except burn skin

They burn very well, but they're really most frequently used as night vision illumination. Night vision (and many more normal) cameras pick up IR very well compared to the human eye. A bright source with low divergence can "light" something up from far away or be defocused for closer.

We used Ir laser/illuminators in the military. It was always cool on night missions to see all the beams through the NVG's

Ah.. I see. And just wondering what the differences are between the wavelengths such as 980nm and then you have 1064nm.. Or the effects of one wavelength over the other

Crystal pumping and scientific research, long distance NV photo illumination is a major use, like an invisible spotlight for your camera, that among many other uses, but you must understand the divergence of the unit and the safe operating parameters before operating.

Military squad commanders can paint targets for NV equipped troops.

If you don't have a legitimate use you should not use invisible wavelengths that can reach the retina. They are dangerous and require extra precaution.

Accidents can happen easily, do yourself a favor and go with a visible wavelength.

Also be aware there is eye safe and non eye safe, some in the 1550nm range will not penetrate your eyes lens and are safer, but read for yourself and know what you are doing, any invisible laser has a higher chance for accidents.

As always Safety First.