In addition, there is an option to override the default cost center rates on a per client basis. You can see this in the below screenshot.
Often what a project requires a resource to wear several hats. In this case they may not use their typical rate. resource can be billed at depends on the project they are working on. You can edit any role and specify the rate to be used on a single project.
In addition, you may want to invoice a role under a different billing title. For example, billing a junior developer as a senior developer. By creating a title based override, a resource can mimic another resource's title. This is often used when a junior consultant might do senior consultant work. This way they are billed at the higher rate. You can also do a straight override and keep the resource under the same title, but using a different rateNot only will the resource have the higher title, they bill at the higher rate associated with it too.
Finally we have rate types. A resource chooses a rate type when entering their time. In the screenshot below, the 200 rate overrides any other setting. The resource's title does not matter, nor does the default rate card. If an explicit rate is not set, like in Regular and Not Chargeable pictured below, then the resource's rate is modified. So for example, in the Not Chargeable row - entering time (no matter what the rate) results in a zero billing rate.