Symbolics systems are used for a variety of different activities. Two ends of the spectrum are (a) the lisp software engineering developer and (b) the graphics professional producing commercial animation graphics. But all users (at least in my experience) can benefit from having extra screen real estate (on PC or workstation or lispm). Obviously those working in color must have a color monitor, but many will be happy with black & white only. There is also the option for any Symbolics user of a single monitor system to use either the standard B&W monitor or a color monitor. But better still is to use two monitors simultaneously.
Hence a typical XL1200 setup would use one B&W monitor and one color monitor to provide double the addressable screen area. This can be used in a flexible way, but typically tool palettes or source code might be on one screen with the application display on another screen.
Although this can be done all on one screen, by flipping between windows, I find it to be quite an advantage to have greater screen real estate. Now you might say that just having a larger single screen with higher resolution would do the same job, but it does not. Going this way, you have to suffer smaller fonts, be more organized in laying out window structures, and you are developing interfaces at a resolution different from that which your intended applications user will see. What is ideal is to have more square inches of display area - hence multiple monitors (that is, screen real estate).
Twin displays can be achieved very economically by using the 3630 with CAD Buffer II (3620 systems cannot support twin or color displays). The overheads to consider are that twin monitors will take up more desk space, but this seems a small penalty for such display convenience. Also bear in mind that you will have to manage more mouse movement between screens if moving the mouse throughout the displays is how you work.
Even more monitors can be supported by high end systems like the XL1200 which includes the basic B&W screen plus an extra color monitor per FrameThrower graphics card installed. But this route is only for the super power user.
Finally, for those wanting independence from the Symbolics B&W monitor, or perhaps just to use an existing multi-synch monitor, there is a console interface box. This is a pizza box which handles the keyboard and mouse I/O, so allowing the system to interface with a choice of other monitors.
In summary, imagine a lisp only code mechanic, he's sitting with his lispm, typing code into one B&W screen. And next to him is another designer, luxuriating with twice the screen real estate at his command, and to some degree twice the ability to get his visual mind around the subject. He types meta-dot to find the code he is interested in, and this throws up the appropriate source in a new window which does not obscure is current point of focus. Most (including me) find this really useful.
But my mind tends to reason visually. Then again I learned my lisp spoiled with resources and opportunities, with no horizon too far. But many were introduced to lisp through college facilities, scant resources, elbow competition, sharing facilities, small windows and academic brain-teasers and a context of threatening exams. It is small wonder that they have not acquired an appetite for larger thinking and bigger screen real-estate. My view of a lisp thinker is like an organist, using feet and hands of a variety of keyboards, the better to wrestle with larger concepts. Not that I begrudge those happy with a penny whistle and few square inches on Emacs. But I've not met anyone spoiled with generous screen real-estate who wanted to go back to tunnel vision.
The reason for this sophist thought stream is that when asked about Symbolics display technology, despite having little experience but with emphatic confidence, most people say they want the minimum. Of course the customer is always right, but there's another point of view in too.
Refs. Monitors - System specs - Monitor photos