Cleaning
Modern, low solid content fluxes are as rule no-clean fluxes. They do not require that residue be removed after soldering. Should the board have to be conformally coated or completely potted, it may be possible that a full cleaning is required. Cleaning may also be called for if high-resistance or high-impedance components are present. In these instances, flux residues may be a cause for changing the properties of the circuit, so that a safe function could no longer be guaranteed.