Of course you do! Your goal should be at least 1 rod in every weight from 1 to 10, as a minimum arsenal.
And to be honest, I am just about there. I lack a 1 wt and 2 wt but have the rest. I find it fun to use lots of different rods but do tailor my choices to fly size, wind, etc. In some weights I have different lengths.
No real solid reason for this many rods. I just like the variety. I will admit I use my 3 wt much of the time for trout and panfish. For bigger flies for pike, musky I most often use a 10 wt.