Pair Programming is for 100% of production code, not 100% of your workday
Pair Programming is intense, mentally and physically. You need to take breaks, stretch, walk around, and hopefully go outside for sunshine and fresh air. Even so, 8 hours of solid pair programming is a very tiring day. That much pairing time may be appropriate now and then, but it isn’t physically sustainable.
Also, although a side benefit of working in a pair is that it helps you stay focused on work instead of goofing off, there are other things you need to do while you’re at work. You may need to make personal calls, shop for a keyboard or a bike, read about some new technology that you might use on the project, or hack up a technology spike. Those activities require some personal space, and most of them require exclusive solo use of a computer. Without a certain amount of privacy and a small amount of storage for personal items, developers can feel dehumanized and unattached to the workplace, like a guest at their own job.
One option is to expect every developer to bring a personal laptop to work with them. If you do this, you will need to provide some physically secure place for them to put their laptop when they are not using it, such as a small locker. A bit of extra desk space to the side of the pairing station is required if a small separate desk is not possible.
Another option is to provide a small number of inexpensive, low-end computers (such as a 3 or 4 year old, semi-obsolete computer that used to be somebody’s main work computer) to act as shared “personal time” workstations. These can be laptops (in which case they need at minimum a bit of available desk space next to the pairing station) or desktops (in which case a separate desk is required).
In either case, it’s necessary to have a private area that can act as a phone booth, and some long term storage available for personal items. A locking drawer unit on casters is good enough for a developer to have a sense of personal space. A tiny conference room or storage room that can accomodate a single occupant can provide enough privacy for personal calls.