The following article contains spoilers from Harley Quinn #22, on sale now.
After Harley Quinn was murdered, she was hesitantly resurrected on the orders of Angel Breaker. However, Harley Quinn #22 (by Stephanie Phillips, Mateo Lolli, David Baldeon, Rain Beredo, and AndWorld Design) makes it clear that the Lazarus pits are no longer a go-to method for the League. In the past, they have always been relatively quick to use the pits to fix their problems. Following its corruption by the Great Darkness and whatever influence the Devil Nezha has over them, it has become clear that the pits' original function of resurrection may not be the only thing it gives to its users.
Harley's emergence with a deranged glee certainly indicates that the temporary madness is still a part of it, but there may very well be more to it. She was lucid enough to speak in complete sentences and as a result seems hellbent on getting whoever it was that murdered her. The look in her eyes though is not one that any hero would possess, suggesting that the corruption within the pits is transmittable to whoever uses them.
As Angel Breaker explained to a desperate Kevin, using the pits was always a risk. Bringing someone back from the dead may be possible, but to play god like that can have consequences. Ra's al Ghul is a living testament to this, having grown more and more insane the more times he went into the pits. In the aftermath of their magic being tainted though, Angel Breaker is no longer certain what could happen to a user. This makes it clear that Harley is probably the first person to use a pit since Deathstroke went in, being used as a sort of guinea pig to determine the consequences of such actions.
Given their mystical nature, and recent contact with the Great Darkness, it isn't too far outside the realm of possibility that the pits might grant someone extraordinary power, but twisting them into a horrible monster in the process. This is, of course, in consideration of someone normal going into the pits. Harley is far from the average person. Harley's physiology was altered by her dip in the chemicals that transformed her, and her mind was never the same afterwards. In the past, the pits have been shown to affect sane and insane minds differently. For example, one time the Joker went in and came out sane.
The same principle seems to apply to Harley to a degree. Rather than come out a raving lunatic, she has retained her ability to reason and speak. However, Angel Breaker's warnings that Harley may have been altered seem to be correct. The look on her face was as close to looking like the Joker as she has ever gotten. The question now is how has she been changed?
Considering that the pits have been influenced by two different entities who harbor malevolence, it stands to reason that negativity may linger within the waters of the pits. Perhaps when a person is brought back to life, they aren't just given a second chance, but also some darkness contained within. If so, then the pits are likely just magical villain factories now. Anyone who uses them would be at risk of internal corruption. Time will tell how Harley copes with her revival, but Angel Breaker's warning must now be minded whenever anyone considers using the pits.