Confusing instructions when to use resistors, Doorbell 3.

Products Video Doorbells
1

I’m planning to replace my old mechanical doorbell with a mechanical chime with a Video Doorbell 3 and keep the mechanical chime.
In the manual, it says that you have to install a 25 Ohm, 50 Watt resistor if you hardwire the Doorbell 3 to a transformer.
On the other hand, at Ring Help it says this in ‘Important Information on Upgrading From Ring Video Doorbell 2 to Ring Video Doorbell 3’:
You should also remove any existing resistors when upgrading. Resistors are not needed when hardwiring a Ring Video Doorbell 3.

The questions:

  1. Am I right that you only need a resistor for the Doorbell 3 (and Doorbell 2) if there is no chime, only a transformer?

  2. Why then should you remove any existing resistors when upgrading from a Doorbell 2 to Doorbell 3?

Many thanks,

Tom.