People who work there will tell you that they provide liquidity, which is a valuable thing to have in markets. I've always been a bit skeptical of how much value they provide there though given that they don't hold on to anything for very long but I'm not particularly informed about it.

Mostly it seems like they scrape pennies off out of the market to enrich the people who work there (they have no outside investors afaik), so imo they are pretty neutral. Not a bad place to be, lots of companies are negative.