Reversible drills are drill that is simply able to be reversed from clockwise direction to counter clockwise direction.
The mechanics of reversible drills are relatively simple. The motor that causes the clockwise motion is often the same motor responsible for the counter clockwise motion. However, in doing this, the process involved is slightly more complicated, and therefore the drill may not operate as well in one direction as the other. This may be consideration, especially if reversible drills are not truly needed.
Not all drills are reversible. Those only intending to use drill with standard drill bit, or set of drill bits, may find non-reversible drills to be their best option.
This is because reversible drills can be considered multi-functioning tool. As such, without specialization, it may not do everything quite as well as specific tools. While this may not be true of all reversible drills models, the lower end models tend to underperform the most, as may be expected with any tool.
The reason why the reversible drills is good for those who wish to use the drill to both drive screws and remove screws is because of the nature of the screw. The grooves of most screws dictate they will go in when being driven clockwise and come out when being rotated in the opposite direction. Therefore, it is important to have drill that can do both rotations, if that is the desire. The advantage of using drill to drive and remove screws is one of power and torque. Many times, an automatic screw driver may not have as much power as drill.
The reversible drills truly make no difference when it comes to drilling holes or sawing holes, as some drills are capable of. If the drill bit gets stuck, simply engaging the motor and turning the drill bit while pulling out should remove it easily enough, even if it is going clockwise. Thus, there really is no advantage to reversing directions in these types of situations.