A smaller body can reduce suction or runtime because it leaves less room for the fan, battery, airflow path and cooling, but compact size does not automatically mean weak performance. Efficient motors and short sealed airways can preserve useful pickup in a small enclosure.
Battery volume creates the clearest compromise. A mini cordless vacuum commonly runs for about 15–25 minutes in a normal mode, while continuous maximum power may reduce that sharply; compare energy in Wh when available rather than voltage alone.
The dust path also becomes tighter. A small bin fills sooner, a compact pleated filter can clog quickly, and sharp turns in the airway increase resistance, so accessible cleaning and a visible fill line are essential.
Choose the smallest body that still meets the real job. Desks and crumbs need little capacity, whereas sand, pet hair and multiple car footwells justify a slightly larger vacuum with better cooling, longer runtime and a wider bin.