Automatic transmission and a manual transmission accomplish exactly the same thing, but they do it in totally different way.
Advantages of manual transmission over automatic transmission–
1. It is easier to build a strong manual transmission than an automatic one. This is because a manual system has one clutch to operate, whereas an automatic system has a number of clutch packs that function in harmony with each other.
2. Manual transmissions normally do not require active cooling, because not much power is dissipated as heat through the transmission.
3. Manual gearshifts are more fuel efficient as compared to their automatic counterpart. Torque convertor used to engage and disengage automatic gears may lose power and reduce acceleration as well as fuel economy.
4. Manual transmissions generally require less maintenance than automatic transmissions. An automatic transmission is made up of several components and a breakdown of even a single component can stall the car completely.
Advantages of automatic transmission over manual transmission–
1. The manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission; the same set of gears produces all of the different gear ratios. The planetary gearset is the device that makes this possible in an automatic transmission.
2. Automatic cars are easier to use, especially for the inexperienced car driver. Manual system requires better driving skills, whereas with an automatic, the clever system does it all on its own. This holds a greater advantage for new and inexperienced drivers and also helps during congested traffic situations where it becomes difficult to change gears every second.
3. Automatic transmission requires less attention and concentration from the driver because the automatic gears start functioning as soon as the system feels the need of a gear change. For car with manual gear shifts, the driver has to be more alert while driving and better coordinated.
4. There is no clutch pedal and gear shift in an automatic transmission car. Once you put the transmission into drive, everything else is automatic.
5. Automatic cars have better ability to control traction when approaching steep hills or engine braking during descents. Manual gears are difficult to operate on steep climbs.