I did an office with a couple hundred outlets. I pulled two spare cables and used them both. The spare cables saved hours of work and we were able to get the replacements in place and terminated so it didn't hold up testing. As careful as you might be, something or someone can snag a cable.
They are as hard to terminate as cat5 and take about as long. I give that job to apprentices. They love it and talk about doing it for a living - for the first day. If they mess up, no one gets hurt and it only takes a few minutes to fix.
We leave a coil of about 20 feet above each outlet. It's nice to be able to move the outlet when the desk is relocated.
We had specs to leave a 20 foot coil over the rack, but that was a disaster with that many data cables and almost as many telephone cables. I prefer panduit or a cable-way to hide a couple extra feet so that end can be re-terminated, too.
