Why use an ESD seat?

I have read the IEC 61340-5-1/2 and we are building a new production area. If everyone who works with ESDS, uses wrist straps while seated, do they need to sit on an ESD chair? (The floor, the tables, the garments are ESD protected)
If they connected to ground via wrist strap, why should I connect them to ground via chair?

Firstly, the ESD chair is not for grounding personnel. The seat may have quite high resistance to ground, up to 10^10 ohms. For grounding personnel, we need a much lower resistance <35 Mohms and this cannot be achieved by contact with many seats. Contact between the seat and body is unreliable because there are layers of clothing in between!

The purpose of having an ESD seat is so that the material of the seat does not become charged and cause an electrostatic field and ESD risk.