I'll third this. I hired a guy, a really bright guy, and put him to work. He was debugging some problem, I think a windows problem, and found the file that co

I'll third this. I hired a guy, a really bright guy, and put him to work. He was debugging some problem, I think a windows problem, and found the file that contained the code with the problem, looked at it, and said "this code is gross, I'm gonna rewrite it". Did I mention he was bright? He was, and he took a look at the history in bk revtool (a graphical tool, shows you the dag, you can left/right click on a pair of nodes and see diffs, double click on a node and see that version of the file). He double clicked on the very first rev and lo and behold, there was the code he was about to type in. He said it was exactly how he imagined it. Hmm, says he. I wonder why it changed. He started clicking around and went "ohh, so on this OS they have that problem". Some more clicks "oh, and windows has this problem with wrapping pids". Etc. Had he not had that history (and had it not be really fast to click around and see it), he would have rewritten the file to be back where we started, losing all the bug fixes. History matters. Being able to see it quickly and easily matters.