Sorry, I guess I wasn't clear.
Kid travels back in time from 1020 to 1010. She changes the past, and a new timeline should thus be created.
Well, a new timeline is created, except it takes the form of a dimension. What is the fundamental difference, then, between a timeline and a dimension? If these were material things which we could examine, how would their makeup differ? Is it like comparing Hydrogen to Oxygen? Is it like comparing Ice to Steam? Or is it like comparing distilled water from Maine with distilled water from England?
To note, the Chronoverse can't have infinite dimensions or there would be no need for a DBT, as every time a timeline changed, it would be a new dimension instead of being discarded.
Rather, dimensions must be rare. CC does tell us how they are formed; Belthasar states that Home and Another world split because there was a 50/50 chance of Kid's change to the timeline suceeding. That's a pretty difficult thing to do; to have dead even chances of one thing or another happening.
So dimensions seem to just be timelines in which a change occurred but the outcome cannot be resolved.
To help illustrate my point, lets say Time is a 4 lane road. Time Travel as it is usually defined is forward or backward along that road. Dimensional travel, however, is sort of like chaning lanes (moving side to side). You still moved on the road, but it was just a different manner of doing so. One is still moving through time, just not in the direction we normally think of. To say traveling forward is fundamentally different than traveling to the side seems to be curiously limited in orientation.
Turn to your left and right and what was "sideways" travel becomes forward and backward travel. So it seems like distinguishing Dimensional Travel as fundamentally different than Time Travel seems like you are insisting that the orientation of a traveler's perspective is key. Hence my original question (part 2); why do you see these as separate things? Is it just because standard Time Travel can produce temporal problems while non-standard (that is, dimensional) travel doesn't appear to produce temporal problems?
Also, a single instance of Traveling between dimensions is problematic, as Chrono Cross is a wonderful example of