What do you mean when you say “slating every take”?

Each time a scene is shot, it is called a take.

Multiple takes of scenes may be planned to capture different angles. Multiple takes may also be necessary due to a mistake made by the talent or crew, which causes the director to yell "Cut!" Each scene should be retaken until at least three "good" takes are re-corded. Then the camera should be moved and a couple more good takes obtained from a different angle.  All this extra footage as well as b-roll will be needed in the editing process.  Ignore the previous 2 sentences at your peril! 

It is better to have the choice between several good takes, than to come up short in the editing room. Never move on to another scene until the takes of the current scene are acceptable. When shooting a scene is complete, rewind the tape and review view the shots and takes of the scene. This additional time is well justified when compared to the alternative: gathering all the crew, talent, sets, props, and equipment for a re-shoot weeks after the initial shoot.

When multiple takes of a single scene are shot, the slate becomes particularly important. The slate is a board or page that is held in front of the camera to note the scene number, the take number, and several other pieces of information about the scene being shot. The camera should shoot the slate for at least 10 seconds before every scene that is shot.  The slate is part of the head of the scene.  When multiple takes of a single scene are shot, the slate becomes particularly important. If, for example, mistakes are made five times in Scene 5, the sixth take is slated as "Scene 5, Take 6." The slate is held in front of the camera for at least 10 seconds, but usually not more than 15 seconds. The countdown then begins to initiate action on the set and to cue the performers.

A take log, or shot log, is a written list of each scene and take number that have been shot and recorded on a particular tape, Figure 14-12. When the performance of a scene is acceptable to the director, the take is circled on the log. Later in the production process, the director can scan directly to the beginning of the good take; instead of reviewing each preceding bad take.  By not having to watch all of the footage - the good and bad takes - and just viewing the good takes, the director can save hours of editing time.