Never.
I gave my scale to goodwill (though, I'm now a bit saddened that it may negatively impact someone). One of the best things I ever did to my body and my mind.
No more "Aw man, but I did so well this week.", "Geez louise, why do I still weigh the same?", frustration, cutting back, and most importantly no more ignoring the signals my body is giving me. Not cool.
If I'm hungry I eat. If I'm full I stop. It is a process. Sometimes I eat too much and feel too full. I own the feeling, I listen to what it feels like physiologically and mentally and I know better next time. You learn the most from your mistakes.
I don't know if I have lost weight since paleo (though I guess one could go by clothe size, but I also believe I've gained muscle, essentially I'm still the same clothe size but things fit differently). I focus on how I feel. I listen to my body and frankly, I highly suggest tossing your scales if it seems to lead to the mental set I mentioned above.
