Is reading app.config expensive?

No question I am yet to be hit by any read speed bottleneck. I am asking to know; if reading app.config frequently is a bad programming choice. I have known of database operations getting expensive. In my case I am not reading my own application's app.config, but of another project's, like this: private string GetAppConfigValue(string key) { ExeConfigurationFileMap fileMap = new ExeConfigurationFi