First off, if the motor is 230V, the issues that load reactors protect against are pretty much non-starters because the spikes and reflected waves they are referring to being higher than the motor insulation voltage rating are not going to be high enough to worry about for 230V motor designs. On most new 230V motors, they are dual voltage, so the insulation is rated for the higher voltage to start off with. That's why a lot of people never see any problems; they are primarily working on commercial and light industrial projects where they use 208V or 230V supplies. If you are putting a VFD on an old 220 or 240V single voltage motor, or any really old motor for that matter, a reactor is an absolute must, but even that may not help in the long run. Older motor insulation is already partially breaking down, the VFD will likely hasten it.
Line reactors protect the incoming line from crap coming out of the VFD. We can debate all day as to the worth, but even if the VFD has an internal DC choke, a reactor will serve to add mitigation of harmonics back into your line.
Load reactors serve 2 functions. They do protect 380 and 460V motors from spikes and reflected waves as mentioned above, but on all motors, they also serve to limit the rise time of any load fault so that the VFD's electronic protection systems can act to shut down the transistors and prevent catastrophic failure of the VFD. When you get a load fault, i.e. a motor winding going to ground or a damaged/failed cable, all of the available power in the VFD tries to flow to that fault in an instant. This creates a high dI/dt (delta(change) in I (current) over delta time) in the transistors feeding the affected phase(s) which can cause other adjacent transistors to fire at the wrong time, causing catastrophic failures some or even all of them. In modern drives, individual transistors are no longer replaceable, so in effect the drive is toast. By adding a reactor, you add an inductive time constant to the rise of the current flowing to the fault in each phase circuit. This can allow the VFD's microprocessor that few extra milliseconds it needs to detect the fault and block the bases of all of the transistors, which prevents them from misfiring in the first place. One save like that is worth 3-5 times the cost of the reactor, so in effect they are always "cheap insurance".
Also, if you have multiple motors off of one VFD, a load reactor is a must, not only for that reason but also to absorb any transients from harmonics and capacitive coupling effects in the multiple motor leads and motors.
