2 more, especially if the project involves retrofitting drives to existing motors:
1) Do a search on "VFD Standing Waves" and read up on this phenomenon if you are not already familiar with it. Part and parcel to the FM that makes VFDs work is this nasty little side effect that can destroy motor insulation, especially on existing older motors. New motors designated as "Inverter Duty" will usually have insualtion material that takes this into account, but if not, you need tpo address it in the system design, i.e. output filters and shielded cable as Besoker mentioned.
2) Motor bearing damage can occurr as a result of voltage being created and building up in the rotor of the motor, then jumping across the bearings and races to find a path to ground. Again, new Inverter Duty motors often will have grounding shaft seals / bushings so that there is a less destructive path for it. But when retrofitting or if not accounted for in submersible motors, the damage can take place in a matter of months. There is not a lot that can be done aside from the grounding, although some types of motor termination filters claim to help, so sometimes the thing to do is either premptively address it in the motor or at least let the user know they may need to budget for that in the near future. I know on deep well submersibles this has turned out to be a very nasty surprise for a lot of people and although it's expensive to pull a pump, it's often less expensive than losing a crop.