The legal strength of a mark is measured in two ways; the mark's distinctiveness and its level of dilution. Distinctiveness is a measure of the inherent qualities of the mark with relation to the underlying goods or services sold, while dilution looks at the number of other companies using the same or similar marks. The more users there are of a mark, the more it is diluted, and thus the less protection that is available for that mark.
In short, distinctiveness measures the degree to which the inherent meaning of a mark correlates with the qualities and nature of the underlying product. Generally, the more distinctive the mark, the stronger legal protection it receives. The distinctiveness spectrum consists of marks that are generic, descriptive, suggestive, arbitrary, and coined or fanciful. Those marks that are suggestive, arbitrary and coined are considered distinctive immediately upon their first use in commerce. Descriptive marks are not immediately distinctive, but can acquire distinctiveness, and thus legal protection, if they are used or advertised extensively enough in commerce to acquire secondary meaning.
Very often, marks that are strong for marketing purposes are weak legally, and receive narrow protection, or sometimes no protection whatsoever. Words that describe the qualities or nature of a product benefit from strong marketing potential in the initial marketing stages, because they communicate instantly to customers what the product actually is or does. For example, "Quick Fix Radiator Mix," tells the customer immediately that this substance fixes radiators quickly. This presumably saves on initial advertising expenses. It is worth noting, however, that the long term branding potential of a mark is probably enhanced with strong legal rights that allow for greater distinctiveness.