The issue with the "keyboard in front of huge monitor" type of arrangement for people who need to get their face really, really close to the monitor is they have to lean far in and hunch over the keyboard, putting their arms in an uncomfortable position. Speaking from my own experience, this causes RSI problems fairly quickly. And the keyboard can't be moved farther back to allow the person's arms to be in a more natural position because the base of the TV or monitor blocks the way.
A monitor arm of the right length and height lets you sit so that the monitor is close to your face, floating at or beyond the front edge of the table, and the keyboard is physically behind the monitor, letting your arms be in a more natural position for typing.
A monitor arm of the right length and height lets you sit so that the monitor is close to your face, floating at or beyond the front edge of the table, and the keyboard is physically behind the monitor, letting your arms be in a more natural position for typing.