Is very useful in sensing the affect of actual performance and heading vs. trimming. When closehauled, the telltails can look fine, but you're really over pointing in some conditions. You can see the actual COG isn't close to compass heading. Visually you can see the effect of weather or lee helm. It's a visually oportunity to get information about the balance of seaway, trim, helm, etc. When pointing on boats I've sailed you can get "good" looking trim to angles up to less than 20 degrees apparent -- if you look at what's actually happening to the boats speed and true course, you see that it's an illusion that the boat is performing like it should. Then, if you compare the "TRUE WIND" direction withe "APPARENT WIND", you can get a mental polar chart in your head of where the optimum is for your boat in various conditions. On our boat it varies a lot more than you'd guess.

Also, having a predictor line (say 10 minute, which we normally set) when coupled with AIS or radar ARAPA information for targets and various other moving objects. The predictor lines allow for an immediate visual sense of closing angles, speeds, and time. You deduce actions without having to depend on "reading" the little print on the display that gives you the digital information.

(Our MaxSee on the computer below has this option graphically for targets (on either Radar or AIS) -- but unless someone is "down" at the NAV Station, we don't have the function at the helm. The information provided visually by the predictor lines really provides a good deal of that information.)

If you're racing (informally or otherwise), you can get sense of your overtaking and crossing situations too.