What is the function of clock frequency of clock source in Qsys?

[Altera_Forum]

When we make a design in qsys, at beginning there is always a clock source module. I try to check the document of this IP but it seems there is no document available. It looks like this module is just passing the external clock to the qsys system. It doesn't not do any changes in the clock frequency or phase. In this case, what is the mean of configuration "clock frequency"? What will be difference if I set the clock frequency or I just not set, but input the same clock frequency? 

 Thanks in advance.

[Altera_Forum]

The clock frequency may or may not be used by modules that are connected to that clock. 

 For example, an SPI controller that is supposed to operate from a 1MHz serial clock would implement a 25x divider if it knew that it was connected to a 25MHz clock. Similar for a UART, etc.  It is an informational parameter, which may or may not have importance in your system.

[Altera_Forum]

--- Quote Start ---  The clock frequency may or may not be used by modules that are connected to that clock.  For example, an SPI controller that is supposed to operate from a 1MHz serial clock would implement a 25x divider if it knew that it was connected to a 25MHz clock. Similar for a UART, etc.  It is an informational parameter, which may or may not have importance in your system.  --- Quote End ---    If this is an informational parameter, that make sense. This can tell other designers what the expected input clock frequency for this qsys sub system.   Thanks very much.