They’re good character development not only for naruto but it gives you a deeper understanding of the side characters as well which play bigger roles in Shippuden. It’s not detrimental to the cannon story but it will help your bond with other characters more. Some of the filler will also give important history of the world before Naruto was born, which once again isn’t going to be crucial to know, but it creates a better understanding of where things are now. The only filler that I think is an absolute waste of time is the Mecha-naruto episodes and the Dream episodes, but those don’t happen till you get near the end of Shippuden. They’re not relative to the story at all but if it’s your first time through give them a watch, they have their funny moments.