Can it be traffic hampering if I change the cos-weight?
The Class of Service (not Server) allows you to give priority to some traffic over other, based on the CoS value. What is important is the relative values between the different CoS.
If you change the value, you are changing the minimum percentage of switch forwarding capacity. Normally, the default values are good for most situations.
Unless you have a specific need, you shouldn't change the values. If could affect traffic if your switch is prone to congestion (i.e., is oversubscribed)
Why is it important to change the cos-weight?
If you have traffic with different latency or bandwidth requirements, the CoS weight allocates switch resources based on the CoS value -- the higher the weight, the more resources that traffic gets.
What is the difference between cos3-weight, cos4-weight and
The default values are the same for each weight. That means they are all treated the same.