Modern military strategy is based on using 'the right tool for the right job'. So are there any jobs (ie scenarios) where a 10cm-tall biped with human intelligence is the right tool?
Imagine scaling up by a factor of 18 everything you might find on the battlefield, and weight proportionally. Most obstacles then become significantly more challenging to overcome, not less. Your downsized humans would move much more slowly and be blocked by obstacles as mundane as kerbstones, drains and tyre ruts. Infantry soldiers they will not make.
However, there are some obstacles that become less obstructive at scale, not more. Barbed wire and chainlink fences are trivial, ordinary drainpipes are navigable, meaning that the sort of building infiltrations you see in Mission Impossible (who actually builds buildings with aircon ducting that large?!) become completely viable.
Your downsized humans won't be soldiers. They'll be infiltrators.
Whether special forces, secretive government agency or high-level crime, your tiny people are best suited to entering non-battlefield environments, where there aren't insurmountable piles of rubble or dangerous obstacles like puddles or fallen branches. Once in place they could easily infiltrate server rooms (where they can get inside server cabinets if required), photograph secret plans (the smallest modern cameras would be similar in equivalent size to video cameras from the '90s) or conduct cyber-espionage or cyber-warfare (deploying a payload on a USB stick the size of a rucksack which they have to hammer into the slot). There are also plenty of poisons of which a downsized human can carry a lethal dose, for occasional assassinations.