Netting 1200 cals- Is it absolutely necessary?

You're 5'1" so fairly petite, I'll assume you have a medium or small frame as well.

Is it absolutely necessary? No one knows what works exactly for you but YOU. So if you hit a plateau then the first thing I would do it look at your net calories and UP them. I know it feels counter intuitive but it does work for MANY MANY people.

I'm 5'7" an hour glass shape with a medium frame. My body does not like it if I net less than 1300 calories for more than a few days in a row and I will stop losing weight. So now that I know that I try and avoid it by eating back exercise calories. I'm most happy at about 1400-1500 calories (NET) a day

As everyone is saying, you don't want to go too low for too long, but it's also dependent on your BMR. At 5'1", you don't have much room to cut calories as your BMR is already close to 1200. I agree with eric that you'd probably be ok around 1000-1100 or so, as 1200 is not the magic number for EVERYONE. You may need to consult a physician to figure out a good daily intake for your body.

It was easy for me to lose weight at 1350 cal/day, but I'm also 5'10" and started at 195, so I was cutting 600 calories below BMR daily. Not to say I wasn't STARVING for like a month as I got used to it, but sacrifices had to be made, and the results were well worth it.

Do you really have to NET 1200 calories? My stats are posted below my signature.
I always make sure that I never go under 1200 calories on any given day. I do use a different site to track calories, since I find it more convenient. Anyway, I typically burn 300-400 calories per workout and only eat half of that back (giving me a 400 cal deficit at the end of the day). So last night, my TDEE (with exercise factored in) was around 1933. I subtracted 400 from it and got 1533, which is the number of cals I ate last night. I haven't experienced any plateaus that some people say is inevitable if one were net less than 1200 cals. Can someone explain? Is this how MFP is set up? Before visiting this site, I never heard of the term 'net calories'.

I'm not sure I follow you. So yesterday you ate a total of 1933 or 2333 calories? If you "factor in" exercise, that is NET calories. If you don't factor exercise in, that is calories consumed (gross calories). I'm guessing you consumed 1,933, expended 400, giving you NET calories for yesterday of 1,533. Is that right?

I'm going to say something a little contrary at this point. But hear me out.

By consuming less than 1,200 calories per day, you risk putting your body into starvation mode. That is not NET, that is consumed.

You should always count all your calories expended from exercise to properly account for your calorie "budget", and to fully understand your surplus or deficit. To do otherwise is only deceiving yourself.

On a single given day, there may be reasons to go under that 1,200 NET calories on a single day. Let's say you do the Ironman triathlon in Hawaii. You may expend 8,000 or more calories that one day. Does that mean on that day you NEED to consume no less than 9,200 (or more) calories on that day? Or else what? Not necessarily. It is more practical to look at it week to week.

I burn 2,000 calories on some days, and 0 on other days. I always eat around 2,200-2,600 calories. My NET goal is 1,580 per day. But I have days where my NET is only 400 for the day. Other days where my NET is 2,200 calories. But when you work out the math on a weekly basis you will generally find that my average NET is about 1,580 calories.

So strictly speaking I'm breaking the Mantra that states "never go under 1,200 calories on a given day". By the way, the MFP tool gives you feedback if you eat less than 1,200 calories in a day, but won't give you that feedback if your NET was below 1,200 and your consumption was more than 1,200.

for me to net 1200 while breastfeeding and working out seems impossible! I have yet to be able to do it! I've eaten so much already today and my net is at 60! I also have been stuck and not losing weight. so I assume I need to eat more but I can't figure out how to get that many calories in unless I eat nothing but junk of coarse!