Fan speed monitoring is important and it should be performed in conjunction with temperature monitoring both within the server and in the server room. Key statuses to look out for are if the fan speed is zero over a long time because that would mean that your fan is broken. If CPU temperature rises while your fan is running at full speed then you have a problem that needs to be addressed immediately. Look at server room temperature at the same time because a high temperature in the surrounding environment means that the fan is just blowing hot air over the CPU.