Why would one download 2Mb+ recording software for just FPS viewing? lol.
Not to mention there would be a FPS decrease due to recording to begin with.
There are also people who can't use FRAPS either due to compatibility issues or just having another better suited recorder (for me Xbox Live)
Knowing current FPS,ping can be beneficial. You would get to know what speed will the player drive,swim and fly at and how good will be the movement and coordinate with your teammates or plan ahead better.
This will definitely be helpful.
Server Sided there is a SAMP FilterScript:http://forum.sa-mp.com/showthread.php?t=288536 While client sided there are various Cleos.Hope this helps