Pipette tips, along with a micropipette, are commonly used to transfer a precise amount of liquid volume from one container to another. When samples are aspirated into the pipette tip, a fine mist or “aerosol” is created, which can get into the pipette. Even after replacing the tip, the aerosol may contaminate the next sample. Carryover is minuscule for most applications. 

However, for sensitive applications such as PCR, even the smallest fragment taken from an already pipetted sample can pose a problem. It would be quite awkward to take apart and clean a pipette after each sample. Pipette tips help to both protect the pipette from contamination from samples and to protect samples from contamination from the pipette.