Thanks for taking the time for such a detailed reply, Philip, but 
everything you say seems to be true of merge as well so I still don't get 
what is special about rebase. Is it just merge+throw away history? And if 
so, why throw away the history rather than just hide it?

On Thursday, June 13, 2013 12:31:07 PM UTC-7, Philip Oakley wrote:
>
>  *From:* David Gdeman
> *Sent:* Thursday, June 13, 2013 7:12 PM
> *Subject:* [git-users] what is the point of rebase?
>
> I've been getting to know git recently as part of some work I needed to 
> do, and I love the easy branching and merging, but I have to admit that 
> rebase is confusing me. I'm not confused about what it does (I don't 
> think); I'm confused about what the point is. As far as I can tell, rebase 
> is just the same as doing a merge and then throwing away some history. Why 
> throw away the history? All of the documentation I can find just refers to 
> making history "clean", but the history doesn't have to actually BE clean 
> to LOOK clean. So why?
>
> Or here is another way to ask the question. Suppose git repositories had a 
> special flag that you could put on a branch that said, "don't show this 
> branch in histories or push it or allow it to be pulled unless the user 
> does something special to ask for hidden branches". Then suppose git had a 
> merge-and-hide command that would do a merge and then set this flag on the 
> topic branch to effectively hide it unless the user really wants to see it. 
> What does rebase accomplish that merge-and-hide would not?
>
> I keep feeling that there must be something else, otherwise why deal with 
> the potential negative consequences of deleting history unrecoverably? All 
> of the documentation on rebase talks about the problem of rebasing a branch 
> out from under someone who is still working on it. So what is the advantage 
> of rebase over merge-and-hide that makes it worth dealing with this problem.
>
> Rebase is a way, within a distributed system, of noticing that the world 
> has moved on since you started on your magic topic branch. 
>  
> So you want your magic topic branch to cleanly apply to the New World 
> Order of the upstream repo, hence you 'rebase', or transfer, your series of 
> nice small changes (commits) to the latest upstream reference point (often 
> tip of master/production), and while doing the rebase, you fix all the 
> conflicts (with the NWO changes) as you go to create a clean sequence, and 
> then you will have a commit/patch series that can either be fast forward 
> applied, or merged without conflict. 
>  
> Obviously (?), having done your rebase you will have to style check, 
> compile and test you new magic code to see if it actually works as planned 
> without any regressions (and fix a few minor mistakes). By which time the 
> NWO has moved on again, so another quick rebase gets you to the head of the 
> queue, and you are awarded tea and medals.
>  
> The other scenario is that you are working on say git itself and you send 
> in patches for review, which end up with fixups and comments, so you have 
> to continue to rebase your own work forward to the relevant start point, 
> especially if there is an overlap with other patch series.
>  
> The "problem" doesn't exist in other, non-distributed, systems because of 
> the restrictive check-out - check-in process which nails both feet to the 
> floor to stop you going round in circles (and limits progress!). Rebase 
> lets you leap ahead and catch up with the latest and greatest code release, 
> or a collaborators code, or wherever. 
>  
> Philip
>  
>

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