OTG creates a link between your mobile phone and other computer
peripherals such as USB flash drive, mouse, keyboard, game pad, card
reader, external hard-drive etc.
It is plug and play, no need of any set-up.
It is mostly compatible with android phones.
Now you don't essentially need a laptop to view what is stored in your flash or external hard-drive. you can do it ON-THE-Go.
It can works well with all Android devices WITH custom ROM/Kernel that support USB Host mode.