I've read the article at wikipedia about IPS panels.
But who should pick a IPS panel instead of a LED panel?
Those are two separate factors (employing the popular car analogy, like two-door/four-door and manual/automatic). You can get IPS with LED.
LED is the backlighting. The alternate is CCFL (fluorescent). LED is better.
IPS is how the pixels work. Alternatives include PVA, MVA, and TN. IPS is arguably the best.