As more and more wind turbines are coming out of warranty, the industry is focusing on making sure that the assets they have in place are in proper running form. If it is the gearbox, the generator, and/or the rotor blades, they need to be inspected and/or checked.
In the case of the rotor blades, if they have had any sort of work performed on them such as repairs after lightning strikes, moisture in the blade, removal and/or addition of coating on the blades, etc. It is good practice to check the mass unbalance. Checking mass unbalance first and then performing the balance job, this will constrain the vibration levels to acceptable tolerances such as the VDI 3934. It will also help reduce the amount of wear on the rolling elements and gears.
Balancing by Alex Nino CRL