Mechanics are trained to sell maintenace to keep the shop profitable. This is a generally harmless way to make some steady money. If you follow the manufacturers recommened maintenace schedule you can't go wrong.
Its hard to calculate the cost of performing maintenace versus waiting for your car do die. A clogged fuel filter can cause premature fuel pump failure. Filter change 115 dollars, fuel pump job 900 dollars.
A clogged air filter can cause the car to over-fuel. Potential damage to the engine from overfueling, loss of fuel economy, potential to damage the catalytic converters.
An air filter is 15 dollars.
You can see where this is going.
If you want to save some money consider learning to do some maintenace yourself rather than paying full-rate at the garage.