It is spurge or spotted spurge. I thought it was nice looking and I need ground cover so I let it grow. That was obviously a mistake. They grow fast and take over very rapidly compare to most of other plants. It is not that difficult to remove them if you pull the tap roots carefully, one at a time, about a few hundred times 
I was lucky I “grew” them in very loose soil. If it is in clay, wet your soil and wait for 15 mins before digging or they will keep coming back. I took most of them out in 1 go and went 2 more times to clean up the rest. It wasn’t bad compare to others.
I grow purslane for salad and soup. It is high in nutrients, lemony succulent like. There is a mexican varietal called Verdolagas, which is popular in summer soup, and available at supermarkets. It is not as spreading as the purslane, has a lighter green color, thicker stems.
I also eat other weeds 
Lambs quarters, dandelion, amaranth, mallow(may be less with mallow because it spreads quickly and have a very deep taproot. It was a PITA trying to pull 1-2’ deep taproots up from clay soil) or whatever the wind brings 
