I've never found much use with the left-right movement but it may be helpful for those that don't know it's a possibility.
I'd bet that because you use a large monitor, and perhaps multiple monitors, and therefore usually don't have much need for horizontal scrolling.
My favorite feature still for the mouse wheel is the middle-click. Clicking any link with the mouse wheel to open a new tab and also if you middle-click any open tab it also closes that tab.
Yes, that's a good one. I first became aware of it a few months ago when I attended a meeting of a local computer user's group and one of the other members and I were sitting at a computer and he told me about closing a tab by just clicking on the tab with the wheel button. It worked on that computer we were using; I also tried it on another computer there and it worked on that one also. But, after that meeting, I tried it at home on three computers and it worked on none of them. However, just last night, I changed a setting for my mouse. Prior to the change, I had it set to Universal Scroll. I changed it to simply Middle Button and then it worked as you've explained. This is on a Win XP system using Firefox and a Logitech mouse.
It still does not work on my other two computers (Win Vista and Win 7). I briefly looked at mouse settings in the Win 7 system, with a Microsoft mouse, but didn't see a setting that seemed applicable to this. I think I'll experiment more with mouse settings on the two computers to see whether I can I make them work this way when using a browser.