Pros: Enhanced driver control relative to automatic transmissions without manual modes
Cons: Generally less responsive and efficient than an automated manual transmission
Summary: If you're shopping for a car with an automatic transmission and you see a term such as "manual mode," "manumatic" or "shift-it-yourself," it likely refers to a regular automatic transmission that lets the driver select specific gears on demand.
It's worth noting that automatic transmissions have technically been "shiftable" for decades. There's traditionally a sequence of numbers below "D" in the shift pattern -- for example, a conventional 4-speed automatic looks like "D-3-2-1." If you leave the lever in "D," the transmission can choose from all four gears. But if you put it in "3," it will lock out fourth gear. If you put it in "2," it will lock out both third and fourth gears. And if you put it in "1," it will only operate in first gear.
Most drivers, however, leave the lever in "D" all the time. As such, many automakers have more recently augmented or outright replaced the traditional shift pattern with a dedicated "manual mode," hoping to encourage more drivers to shift for themselves.
Manual mode actually provides more control than traditional shiftable automatics, because it lets you choose a single gear and keep it there. Think of it this way: If you shift into "3" on that old-school 4-speed automatic, it simply tells the transmission, "Don't go higher than 3." That means the transmission is free to use 1 and 2, and not necessarily when you expect it. But if you select "3" using manual mode, most transmissions will hold that specific gear as long as possible. In this respect, it's very similar to a true manual transmission.
Manual modes vary in detail, but most involve a separate area of the shift gate with joystick-style shift action between "+" (for upshifts) and "-" (for downshifts). A growing number of vehicles also offer shift paddles, which are mounted either on the steering wheel or behind it on the steering column, putting this "+/-" functionality at your fingertips.
What it means to you: As a driver, the more control you have, the better. Whether you're in the middle of a snowstorm or driving up a winding mountain road, you don't want your transmission to catch you by surprise with an untimely shift. The beauty of manual mode is that -- in theory, at least -- it takes the unexpected out of the equation.
Keep in mind, though, that a good automated manual transmission may be an even better choice.