Herbs don't required too much root space and in my opinion easiest tended to in containers. You really don't need much more than a 1 gallon for most herbs (at the minimum), although a large container with a assortment of herbs is very nice, In containers they are also attractive, smell good and decorative in proximity to a patio, porch or kitchen (I guess that would apply to a small garden of herbs also). I always felt that maintenance and pest monitoring was much easier in a container also. The only real disadvantage is if you goal is to grow a large volume, then containers are not so good.
In your post you say " I have heard that giving the roots more space (unlike a container) could result in better greens."
This sounds more applicable to vegetables rather than your typical herbs such a Marjoram, Rosemary, Thyme, Savory and Sage... There are a few herbs that I do see applicable to your statement, herbs that can be ground herbs in addition to container herbs, those would be Parsley, Oregano, Green Onions and Cilantro. They get used in larger quantities with some people, some grow and mature fairly quick and bolt easy so one often would want many planted and to plant them in cycle to ensure there is always some on the ready. With Marjoram, Rosemary, Thyme and Savory a few plants can go a long way and can easily be maintain in containers. Basil is kind of between the two groups but I prefer it in containers.
