M_Boats: sliding gooseneck

Always the questions. My 2004 M17 has a sliding gooseneck that allows the boom to rotate maybe 5 degrees from vertical in either direction, but the boom can rotate 360 degrees if it is pulled aft against the spring in the fitting. Anyone know why it is made this way? Is it just a shock-absorbing mechanism? Thanks, and Happy Solstice! Puzzled in Snow Country