Split-brain, or what are the hemispheres for?

I see behavioral studies of patients with severed corpus collosum describing one or the other impairments of recognition functions.

"Speech" and "Visual Recognition and "Tactile Recognition" are easy-to-label groups of function. Simply noting that the majority of such are localized in different hemispheres yields the obvious point: that coordination is interrupted when you cut the connecting nerves.Possibly you could have just as well localized  them on one side. Perhaps there is an advantage to having two thoughts about the same thing?

Is there an origin of two brain hemispheres? I want to think there is some "first" hemi-brained creature with some "first" function not possible with only a single brain. But the logic is weak. Hemispheres could have arisen as redundant organs, followed by specialization.

Are there comparable creatures with and without dual hemispheres? If so, are there functional behaviors which differ and seem to have been enabled by the dual hemispheres?

Microsoft are you listening?

[Surely not]. I totally buy into the idea that we can structure information in terms of rectangles - nested, overlapped, chained, whatever...and that it is the same as the hierarchical structures that come so naturally. But you implemented it wrong, and a desktop covered with open folders  (after a few minutes work) is a mess.
Get rid of double clicks, use left click to activate. Right click for selection and everything else. Double click now can be mean: activate and keep (f-in) window open behind me...a rarely used option.
And while I am criticizing, why don't you build something for old people? And why don't you build something where I feel like I am in control of everything from unasked for updates to pop-ups and scams? Not to mention our government watchers.

A nice example of the cloud jet trail phenomenon

I can now refine the question:

If jet trails diffuse more slowly in areas of higher humidity, what is the difference between the visible cloud where the jet trail diffusion is slowed and the invisible part around the cloud where it is equally slowed?