the dual/gate is known as the his/her shifter. and by gated means the following.
on one side it is like a normal shifter. but rather than push a button down to move it out of gear you have to move it sideways and down to go threw the pattern. when you get to netural you can then move it to the right and go down the his side or racing side. on that side you can shift each gear without over shifting. meaning your in 1st gear and you hit the shifter as hard and fast as you can you only go to 2nd gear and then hit it again and oonly move to 3rd and then hit it again and you only go to 4th gear. Now if you take your stock shifter and put it all the way down into 1st gear and then hit shifter forward to the next gear as fast and hard as you can you will end up into neutral.
now as you ask the purpose of the gated well it is same pircinples as a rachet shifter being able to manually shift an auto without over shifting. 1 gear at a time. this is designed for racing. does it really help, no but it is just cool as hell to do.
another explaination......
The Hurst Dual/Gate shifter, also known as the "His and Hers" shifter, was standard equipment for the Hurst/Olds performance package. The proven Hurst automatic shifter was mounted in an Oldsmobile sports console. Dual shift patterns provide the ultimate in street/strip control. It's strictly automatic on the left side and as precise as a fully sychronized manual control on the right. Hurst's positive latching mechanism and Neutral lock-out takes the guess work out of gear changing, going up or down. There's no possibility of missing a gear. No chance of overshifting into Neutral and maybe blowing an engine. It means you've got a real choice. You can be as shiftless or as energetic as you like. You can rely on that brain beneath the floorboards or you can trust your own reflexes. The lady of your life can drive automatically, while you remain boss of the block with the manual control.