I bought a 10' 4wt last year and looked at / handled several different 10' rods during the process. I had previously fished a 8' 4wt most of the time.

The thing I noticed first with 10' rods was the extra weight. A 10' rod is probably going to be almost 50% heavier than a 8' rod of the same line weight. Furthermore, the longer lever can make the rod feel tip heavy (depending on the rod and the reel you use with it). Lastly, some of the 10' rods, and it seems like especially those targeted at Euro nymphing, are quite soft / slow which may or may not suit your style.

All that said, I really like the 10' 4wt that I eventually bought. The extra length really helps with line handling and mends. It's most useful on larger water where I'm making longer casts, but it use it a lot more than I expected on small streams.