Latches are memory devices and can store one bit of data for as long as the device is powered.
As the name suggests, latches are used to "latch onto" information and hold it in place.
Latches are very similar to flip-flops, but are not synchronous devices, and do not operate on clock edges as flip-flops do.
The reason for using the latch in an output port is simple, we do not want to lose the result of any operation.
So, in order to not lose it, we use a latch, so that it holds the information as long as new information is overwritten onto it.
An 8-bit latch can be used to interface the output of a microprocessor to other devices.
The 74LS373 octal latch and the 74LS374 octal D flip-flop are popular microprocessor interface chips.
Tristate buffer is commonly used to interface input devices.