This site contains many discussions about fuel additives. The general rule of thumb is that always change the oil after using them. Even Techron, I believe on the bottle suggests this. The reason is particles are displaced in the combustion chamber and wash down the cylinder walls into the oil. Your oil gets "diluted/contaminated" by the particles and the "extra-stringent" fuel reducing your engine oil's normal protective properties.
I have run several bottles through the fuel, back to back to eliminate dirty injectors. You shouldn't have to add with every tank of fuel.
Depending on your car and its mileage, if using a fuel injector cleaner doesn't cure the problem, you should seriously consider replacing the injectors. It isn't that hard a job and you'll know that area of your engine is right.
I run a bottle, maybe two, through a couple of tanks of fuel maybe twice a year, right before an oil and filter change.
Hope this helps.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)