You need to be board certified. I don't know of any groups where you can coast on the BE status indefinitely. Some groups have hard clauses written into their contracts about the time frame you have before you have to get certified. Others will just informally pressure you until you take the test or leave. For most groups the contract with the hospital requires BC docs so they aren't going to mess around with something that could scuttle the contract.
Ok, I forgot I was in the general forum and not the EM forum (and I am BC so it can't be that hard). The above goes for EM. For other stuff the reasons to be BC are that you are more attractive to pt's (as a doctor, BC does nothing for your looks 😉 ), you get more referrals, you are better off in a lawsuit, you can get priveledges much more easily and probably most importantly you can bill more effectively. Many insurers won't reimburse people who aren't BC.