What I call "scratch" recordings are usually just little bits that you record on the fly, often not on your good gear or with the focus being on great sound quality.  Pretty much anything that can record at all will do fine for these.

"Scratch" in this case is like a "scratchpad" or a scrap of paper to doodle on and jot down an idea right when you have it.  The priority is to just catch the idea, and you want to use gear that is already set up or that you can turn on and use really fast.  Like in seconds, since even a few minutes can be long enough for an idea to manage to evaporate sometimes.  

Not a problem if you usually play and practice in your home studio or something, but for most folks it can be a good idea to pick up some sort of little inexpensive pocket recorder or even a cheap old cassette recorder from a yard sale or whatever.  A portable option that you can keep handy anywhere you may practice/play is a good option even if you have a fairly elaborate home recording setup.

Now, you may think "Oh, I don't ever write any music, so this pointer wouldn't apply to lil' ol' me.."  And you would most likely be wrong.  Often in practice, even the folks that are playing just from written score will end up (even by accident sometimes) doing the bowing or a little embellishment differently sometimes.  And sometimes, at least with some work, it could sound good.  If you can pause your practice and record that, along with your spoken explanation of what you are doing, then you can do it again in the future.  Even if it maybe doesn't fit better in the piece you're working on at the moment, it becomes a bit that you can try in other places. 

If you don't record it with some explanation that you can understand (nobody else has to, since nobody else ever needs to hear the "scratch" recordings), then you may find yourself a day or two later trying to remember how you did that little bit. 

If you catch it in a scratch recording, it becomes a bit or trick you can try in places where you think it may work, and see how it sounds.  Like another brick to build with.  But if you don't grab it when you happen across it, then you're throwing away what may have been a little bit of progress in your development and your sound, and it becomes more like a brick left in the wall between you and your next breakthrough.