As the U.S. Army debates whether to equip their M1 tank with an autoloader (and reduce the crew from four to three troops), they are facing another problem with crew size. Over the last two decades, the M1 has acquired a lot more sensors, and commanders are using tanks increasingly as mobile, armored, and heavily armed, observation posts. The thermal (FLIR, or forward looking infrared radar) sensor in the M1 is particularly powerful, but now all four members of the crew have a thermal sight, plus a rear facing day/night vidcam and a thermal sight for the 12.7mm machine-gun on the top of the turret. There is also an auxiliary power unit, so the M1 can sit in one place for a long time, run its sensors, and keep the main engine turned off.
While the thermals are designed to spot other tanks over 3,000 meters away, they can detect individuals at shorter distances (1,000 meters or more.) But like UAVs, while the thermals can be watching for long periods, the people staring at the screen, waiting to spot something of interest, get tired quickly. UAVs use several crews, so observers can maintain their diligence. While tank crew members can take turns, three troops sharing that duty will wear out faster than four.
One long promised solution is image recognition software, that can identify a suspicious moving shape and sound an alert. This stuff has been in development for decades, and is now in use for some applications. For tank thermal sights, not quite yet. So for now, more people in the tank available for manning the thermal sight, the better.