Hi.
I was wondering if a person could not go by the yarn weight system? 
Do you guys always go by the standard yarn weight system?did anyone here ever use a different yarn weight than the pattern? 
Like i want to use a different yarn weight to make a pattern bigger for a blanket for example.
Yes there are times when i will use a different weight you just have to make sure you adjust your guage, size of needles used
Generally I follow the pattern, but with things like blankets you can usually change weights.