The majority of kitchen exhaust fans are the round silver aluminum type located on the roof, which sit directly over the top of the duct and discharge the air straight up (known as an "Upblast Fan"). This type of fan should be installed with a "Fan Hinge" which allows a service technician to tilt the fan back to a 90 degree angle. The titling of the fan provides proper access to the fan blades and the ductwork leading to the kitchen hood. Many fans are installed with insufficient electrical cable to tip them or are tarred to the roof. Fans that are tarred, that have insufficient cable, or that do not have hinges should not be tipped for fear of damage to the fan. These systems do not meet the NFPA 96 standard. This means the bottom of the fan and the ductwork below will not be accessible for cleaning. The NFPA 96 standard states this type of fan shall be hinged. If your fan is not hinged, you should inquire as to how your cleaner will be accessing the fan blades and ductwork during the cleaning process.
Removing the fan and placing it on its side during the cleaning process will create unnecessary wear and tear on the fan, the fan wiring, and the fan motor which will lead to more significant fan problems.