Why are disposable aprons used?
The US CDC has suggested using
Disposable Aprons over gowns as an additional measure to provide protection from contamination of garments during aerosol generating procedures.
Disposable aprons are used to prevent the uniform becoming contaminated. They are also used to provide a clean barrier over your uniform for aseptic techniques such as dressings, urinary catheterisation, etc.

Disposable single-use plastic aprons are therefore recommended for general clinical use when close contact with the patient, materials or equipment may lead to contamination of uniforms or other clothing with microorganisms, or when there is a risk of contamination with blood or bodily fluids.