This value is taken into account when carrying out pitstops during sessions. The higher this value is, the faster pitstops will be. Having fast pitstops can give a strategic advantage to a team by making sure that the drivers lose less time in the pits than their rivals. This value can be increased from the Preparations page.
The overview panel also shows the number of parts being produced and those finished for each part type. This is given in the form <parts in production>/<parts produced>.