The omission of any filter will have a detrimental effect on an engines longevity.
With regards to the fuel system, there is no guarantee that the fuel supply is perfectly clean. An excess of water in the fuel can result in lower power output, corrosion of the lines, injector damage and reduced combustion power. There is also the risk of other contaminants (dust etc.) which could cause injector blockage and/or failure.
Day to day running of an engine causes wear and tear on the mechanical components. Carbon deposits from combustion, metal particles from friction wear, or anything else that ends up in the oil sump would be recirculated through the engine causing premature wear to the oil pump, resulting in lower oil pressure and more wear to all engine components if there is no filter.
Air filters remove airborne dust. No filter would allow contaminants into the combustion chamber and cause premature wear of the bore, pistons and rings, thus reducing engine performance and increasing carbon build up. Which can end up in the oil sump, and if there is no oil filter? (See above).
All may be fine to the naked eye initially, but every day the engine components wear that little bit more until one day they fail.
Whilst it is your choice to go without filters, the few dollars you save will drastically shorten the life of your engine, costing you a heck of alot more in the long run.
