How do errors, that are shown in reports, effect performance? 

How do errors, that are shown in reports, effect performance? 

  
Some reports have a column called errors, (Slow Timers, Slow Web Reference etc), I was wondering what kind of toll does this take on load time, processing and in general preformance. Do these reports contirubute to the avg. time or not? Is this something I should worry about ? 
In general, no. The time needed to log such a warning is extremely small compared to the time a slow timer/web reference etc. uses. Other logging however, may affect performance, e.g. logging of extension use. But these can be turned off.