>> >> Keyboard is the primary scroll device.  Thus I want to turn
>> >> auto-hscroll-mode t by default.
>> >> 
>> >> Occasionally I want to use mouse as scroll device.  When I use mouse,
>> >> I want to set turn auto-hscroll-mode nil, especially after
>> >> implementation of <wheel-right> and <wheel-left>.
>> >> 
>> >> When I come back to keyboard, I want to set auto-hscroll-mode t again.
>> > 
>> > This looks like a very specialized use case, so I'm not sure we need a
>> > solution for it in Emacs.
>> 
>> I see how you see.
>> 
>> How I described, is similar to how spreadsheet program reacts.  It
>> lets user scroll both by <wheel-left> and <left>.
>> 
>> I very often edit a buffer with long and short line (for example,
>> LaTeX table), using mouse and keyboard.  However, as you infer, this
>> can be already very special.
> 
> What makes this special is that you want Emacs to work differently
> depending on the input device.  Emacs normally makes a significant
> effort in the other direction: to produce the same behavior no matter
> where input came from.
> 
> I'm not sure we want to have such unusual behavior as part of Emacs.

Can you take a look minor-mode that I want to invoke by hook?  I still
think this is potentially useful to mouse-loving cloud using
<wheel-left> and <wheel-right>.