Why keep a project log?

Of course you keep all your syntax, output, and logs from your analyses, but why should you keep a separate log of your work, and what should it look like?

Why? 

Because your analysis logs won't tell the whole story. If you're good about commenting your code, they can tell most of the story, but there will inevitably be some question or insight that comes up after you've run things. At this step, it's probably easier to update notes in a Word file, text file, Excel file, or some place external to your code.

What? 

The format isn't too important. Use whatever program you find easiest to use. I use OneNote b/c I like how it lets me drop in pictures, etc., and automatically inserts URLs from things I copy and paste from the web. But it can be slow at times, and has more than one needs for a log. I've tried Excel before, but that's just too restrictive for me. It's good for other kinds of logs, but for a general project log, I like to have more free space to write.

What goes in this log? Anything you want to remember for later. I write a short summary of what I did during the session/day, and list/highlight open questions and next actions. If I made big decisions, I'll document that (though I like to have a decisions log, too). If I have key output or a finding, I'll add that.

Think of this as your "captains log"...record all the highlights and puzzling issues of the work, as well as major insights and new ideas.