In very general terms, the contamination found on termini end-faces will fall into three basic categories: particulates, oils and salts. Each requires specialized methods for proper removal.
Particulates are solids usually held on the end-face by electrostatic attraction. Static charges will actually attract dust particles in the same way a magnet attracts iron filings! The best way to clean particulates is by dissipating the static charge that attracts the dust particles and locks them in place. This can be done with a specialty cleaning fluid that actively dissipates static charges.
Oils are harder to clean. A well-engineered cleaning fluid will selectively dissolve oils found on the fiber end-face without damaging materials used to make the connector, its housing, or surrounding components.
Salts, on the other hand, are not necessarily fully removed by cleaning fluids alone. While cleaning fluids may quickly dissolve oils and rinse away particulate, they frequently dry and leave salt remains behind in the form of a white residue that can be very difficult to remove. The absorbency and mechanical action of a wipe or swab is best combined with a cleaning fluid to fully eliminate oils, particulates and salts that would otherwise be left on the termini end-face.