This prevents too much power from being used directly from the motherboard. The motherboard can sound an alarm if the fan fails. This feature is good for fans that are critical to system health such as CPU fans. Pulse wires can only be used with 3 pin connectors since those are the only fan connectors that attach directly to motherboards. Check your motherboards specs to see if your system supports RPM monitoring.
Most fans have either a ball bearing or a sleeve bearing.
Ball bearing fans are more reliable due to reduced friction. Sleeve bearings have a shorter life, but they are slightly more quiet than ball bearing fans. This is because ball bearings produce a slight rattle. Hydro-wave bearings are similar to sleeve bearings except they ride on a cushion of lubricant to reduce friction. This design is as quiet as a sleeve bearing fan and as reliable as a ball bearing fan.