Is losing 3 pounds a week pretty good for weight loss?

That's four and a half times the rate I've ever lost weight at. If you kept it up, you'd lose 156 lbs in a year. From what I've read, you'd have to be practically starving yourself to obtain such weight loss. That is not a good idea. It seems to me that you should actually be losing -less- weight, not more.

At that rate you'll be losing fat and muscle too fast resulting in crepey or saggy skin.

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I said yes because i didn't want to encourage more weight loss, three pounds/week seems like a massive amount of weight to lose, and it begs the question, "what am i losing to lose this weight?" Because a loss of weight is a loss of mass, and a ton of mass lost makes it hard to keep track of what was actually lost. Don't starve yourself because it is not too wild of an assumption that you want to be alive by the end of your weight loss journey.

That's actually too much, unless you're like MASSIVELY overweight like 300+. 1-2 is normal.

Try 1 lb per week or 4-5 lbs per month

Not really, a caloric deficit of that high impacts you more physically than losing the raw weight.