If the drill has an electronic torque limiter then the increased current caused by the switching will probably be limited.
If it is an electronic drill, reversing is achieved by means of a lever switch just above the trigger switch.
What happens is that when an electric motor is turned off, the magnetic fields within suddenly try to collapse. The very act of collapsing magnetic fields will then cause another current to be induced which will try to maintain this magnetic field, which then tends to collapse more slowly.
This sudden collapse of fields also causes a large reverse voltage to be induced, and this is directly proportional to the rate of change of field.
When you switch off a motor the reverse voltage is often quite significantly larger than the original supply voltage so the motor winding insulation has to be able to cope with this.
This rate of change will be very much faster than usual if you reverse the polarity switch, hence the reverse voltage induced is going to be very much greater, the motor will stand it in all probability but you would be putting the motor winding insulation under much greater strain. If the motor is already hot, the drill fairly old and well used, you risk shorting out some of the motor windings.
Drills such as this are very robust, it generally takes a lot of ill treatment to damage them, usually things like the switch fail rather than the electrics.
Its possible that the larger current caused by reversing in this way might kill the switch if it is already aged.
The brushes will arc during the sudden slowdown phase and might chip slightly at the edges, which would reduce power and efficiency slightly.
If the drill has mechanical reverse, where you change cogs in the gearbox via a lever on the casing, you stand a good risk of buggering it up completely.