In The Terminator, the T-800 is stalking Sarah Connor, when he busts into the hotel room where she and Kyle had been staying. He immediately starts to spray bullets, and since Kyle and Sarah are gone, the maneuver is quite obviously fruitless. Granted, it's not as though the terminator wastes thousands of bullets, but still.
Is there a good in-universe reason why the T-800 would blatantly waste bullets?
T-800 on the hunt (starts at 0:41):
He doesn't 'waste' those bullets. His fire pattern (sweeping left to right and taking in the bed and free areas to the left and right) is inhumanly efficient. The fact that they're not there isn't his fault and had they been in the room, even in defensive positions or under the covers, they would have been caught in the spray of gunfire.
The machine stepped into the room and sprayed it efficiently with automatic fire. Bullets thudded into the bare table — collapsing it, splunked through the easy chair — geysering chunks of wadding, and found the bed, ravaging it until the smoking carcass of mattress and metal frame could hold no life.
Terminator reloaded, then looked around.
An error had been committed. Terminator’s digitalized view of the interior revealed every object in stark relief, every object but the target. Room number double-checked.
The film script suggests that he may have been confused by the pile of pillows on the bed.
The door is KICKED OPEN.
Moving inside.
The assault rifle sprays the room, exploding the indistinct forms on the bed. Staccato glare. Approaching the bed. Nothing there put the shredded remain of sheets and pillows.
And sure, he could have waited until he had a positive ID on his target/s before attacking, but those miliseconds of delay could have led to it being disabled.
The T-800 was on the verge of no longer being able to pass as human. It had to wear sunglasses to hide the loss of its eye and the damage to the flesh of its face, its eyebrows had been burned off, and the decay of its flesh was producing a strong smell that was already drawing comments from humans:
[I]n original timeline, early version of living tissue can necrotize if damaged as after being shot multiple times during the shootout in the police precinct, the original T-800's skin had a noticeably pale color and flies were sitting on its face. At this point, the janitor of the building, which the T-800 was using as a safehouse, commented on the smell of decay coming from T-800's room: "Hey, buddy, got a dead cat in there, or what?" Hence, the early version of living tissue apparently may "die" or at least undergo extensive necrosis.
— Terminator Wiki: Living tissue
The Terminator had also needed to repair damage to the mechanical components of its arm; it couldn't count on the repairs holding, or on being able to withstand additional damage. With its combat capability reduced and its effectiveness as an infiltration unit about to expire, it had this one last chance to complete its mission, and apparently it chose force over finesse as its "Hail Mary pass".
The T-800 had infrared vision capability, which it might have been using to target hot spots in the room, such as the bed that Sarah and Kyle had recently warmed. The Terminator's point of view doesn't seem to show heat — eg, the man in the parking lot at 0:31 does not show the bright and dark patches typical of an infrared view — but maybe that's what the red imagery is supposed to represent even if it isn't accurate to infrared in real life.
