It looks kind of cool, especially if there is an underwater light shining at the stream of bubbles that are coming from your return lines into the pool.
Actually, it indicates that you most likely have a suction side leak in your pool plumbing. “Suction side” means that the leak is before the circulation pump, and could be a pin hole in the plumbing, a bad seal on the pump, or simply a joint or flange set that is allowing the outside air to be pulled in by the force of the water in the line.
The force of the air can damage your impellor so it is a smart move not to leave it for too long. Best way I know is the “wet T shirt” process; get a wet T shirt and, with someone standing by the side of the pool to observe the bubbles, begin by carefully wrapping the T shirt around each join in the pipe beginning from where the line enters the mechanical. If you are fortunate the bubbles will stop when you close off the area with the leak.
If luck does not prevail, then you may have a larger issue with a leak in an underground pipe. The only way to locate this would be to use a professional service who would probably use ultrasound.
Remember that the bubbles are indicative of a leak before the circulation pump.
Usually, the bigger the leak the larger the hole/break in the line, except if you use a chlorine generator, which will break the oxygen bubbles into millions of smaller bubbles.