It harms Nothing and is actualy good for the motor. Startup is the hardest few seconds on an engine when the cilinder has no oil.
My 91 always has done it and at its last emissions test it looks like it could go to 400000m before it pollutes past the legal amount.
Did you know many race cars have a oil air pressure assist for startup on race cars. Read up, startup it is said causes 50% of a motors wear, that little bit of oil that leaked by the valve seals and is fumimg like a 2 stroke is free lubrication of your cilinder walls. My 105000m 4 cil burns 1/2 -1 qt in 5000 miles, there is your true indication of an engines condition, that and the pollution test I must do every year.
I actualy like what it does, my plugs burn clean, I burn no more oil than a new car, my compression, milage and pollution test are great. Before catalytic converters many "motor heads" put oil in the gas and it was sold as "Top Oil" for immediate upper end starting lube. Be happy, it actualy helps you.