MediaPost: Why Reach & Frequency is Important To Online Advertising
If we believe that the medium CAN actually be used for the purposes of branding, then the only way to carry on the rhetorical discourse of convincing an individual that a particular product or service will alter their relationship with the world around them for the purposes of moving product is to proxy the appropriate number of people that must be touched by the message to get X widgets sold through the use of reach. That's essentially why it is used in traditional media, and the same would hold true for online. Otherwise, online as a medium, will maintain a more ghettoized placement in the overall marketing mix and always play the role of a medium separate from all the rest, always being on its own flow chart, if you will.
The Internet is a unique medium, yet at the same time it is just another media choice when crafting a media plan. For the effectiveness of a media plan, and the media choices within that plan, to be evaluated, a common method of measurement must be used. One of those forms of measurement is reach and frequency.
Rightly or wrongly, this form of measurement is the most common to determine how various options within a plan contribute to the outcome. For the Internet to be considered as an equal player in these initial planning stages, it must adopt models of measurement that work with other media. Reach and frequency will not replace other forms of measurement the medium already has, it will just allow the medium to be more easily evaluated in the planning stages of the game.