Small value of the "tickInterval" option results in too many ticks that cause the browser to be unresponsive. (To reproduce by changing the series data from "500" to "10000" at below jsfiddle link.

http://jsfiddle.net/xvun8/1/

So it would be helpful to have the max tick number as a cap.
If the data range is too big and tick interval is too small which makes the tick number too big, then the max tick number is used to prevent the unresponsive behavior.