I didn't get it either... at first. Then I saw a post on here, where someone mentioned that if you SLOWLY turn on the highs and hold it at the right spot in between, you can keep both on... so I tried it, and it does improve vision.
You could do that on my old Dodge with its (2) 9004's too... but it didn't offer much difference... on the Alero, with it's 4 bulbs, the difference in projection is much more noticeable!
Don't get me wrong... if I'm on the Garden State Parkway doing 70, it doesn't make much difference, because I'm looking way ahead of the car anyway.
However, if I'm doing say, 35, on a pitch black rural back road with that speed limit, and it is deer season.... I want to see BOTH way ahead of my car, AND ALSO still have that brightly lit area of road directly in front of me. Deer can be a hazard running out anywhere from 1/4 mile to 14 feet in front of you! Why should I sacrifice light directly in front of my car to see further down the road?
A simple mod offers both.
My wiring is still stock, but I'm actually thinking of doing a HI = HI + LO myself, but not the way I've seen suggested on here, modifying the cars stock wires. If I do it (and I'm not sure if I want to bother) I will do a setup with relays and a battery hookup, so that I can both: a) simply undo the process by just unplugging it, and also b) I could safely run some eBay harness burners, just for kicks!