The office allows you to appoint staff members as head of your other facilities. It also has several other functions, listed below.
The office increases the interest rate you receive over your money. Without office, you receive 3% (yearly), with the office this can increase up to 10%. The interest you have to pay when you have a negative balance is not affected by the office.
The office also reduces the transfer costs. Without an office you only receive 90% of the transfer fee after selling a player. With the office this can increase up to 95%.
For each two levels of the office you can also have one extra player in your reserve squad.
Finally, the amount of money you receive from sponsordeals is increased up to 50%. You do need to manually sign a new sponsordeal after upgrading your office.
Starting in season 17 you can appoint staff members. When a staff member is added to a facility, the facility receives a bonus.
You can make any of your players that are at least 30 years old a staff member. You can also appoint staff members who weren't players. The skill of a staff member depends on the experience he had as player and the time he worked as a staff member.
The more skilled a staff member is in the field he's working in, the higher the bonus to the facility. Staff skill ranges from 0 to a maximum of 10.
You need to have one facility at level 7 or higher before you can build the office.