REC's are just a bit more abstract. Emissions avoided are as good as emissions removed from the air. First rule of conservation. So instead of contracting Carbon Engineering, who is still working down their cost per ton, I pay out of my pocket to install solar panels on the roof of somebody else's factory, averting the carbon emissions their electricity demands would create. So again, in net, flying my planes produces carbon, but buying a ticket on my plane also pays for solar panels that save carbon.
Wait, sorry, it's one more level of abstraction- I didn't actually install those solar panels, I just paid a chunk of money to somebody to help them install solar panels when they couldn't otherwise- it's a pain to do things in units of "one whole solar installation", and I don't want to worry about the details like which roof to put them on.
Sure, it would be great if we could halt all carbon output today, right now. But we can't. So REC's help send more money to the renewable energy industry, bring more capacity online faster, and advance their R&D quicker than would otherwise. REC's aren't a tool for getting us to zero; they are part of getting the ball rolling in a downward direction.