Thermal printers will accumulate paper flash and label residue, which will impede the heat transfer necessary for an error free print. Use a cleaning card to clean the printhead and platen rollers of thermal printers regularly to increase the life of your equipment.
By not cleaning, you risk increased:
Wear on the printhead
Faded receipts or erroneous barcodes
Need for reprints
Manpower associated with broken equipment
Damage to printer due to "self-help attempts"