I get a lot of success out of it as a mixup tool. B1 by itself is a great tool for neutral. It's a good antiair and it can stop anyone in their tracks that try to run or dash in on you. The best part about b1 is it's recovery. It recovers relatively quickly on whiff, so you can just throw it out and not worry about getting blown up.
Now for the mixup. B1d4 is high, low and leads into solid damage and a setup if you want. However, if you notice people are blocking low every time and punishing you, do b1, run cancel>> b2 instead. It's essentially a high, overhead, similar to what johnny does with 113 and 11, f2. It's great after hard knockdowns like 121 and 123 (corner only), since you have enough time to whiff b1 and still block a reversal if you make the read. Oh, you can always b1, grab too.