[Dr. Sivana]

They were both just annoying as hell. More annoying than they were funny... Just MHO.

They were absolutely essential to make Groucho's world possible. As it is, the suspension of disbelief is BARELY possible in the early movies, but Harpo and Chico are needed to make it looks like the Marx Brothers have taken over completely. Someone wrote that even Zeppo was needed as the interface between the Marx Brothers and the real world, in that he was "normal" but had an idea of what the other brothers were about.

[tlozo]

They were absolutely essential to make Groucho's world possible.

Yup, Duck Soup would have lost much of its humor without them.

[stanne]

The story is, their parents had to leave them alone for a day and it was a lot of unchecked energy. 5 boys

The scene in ‘Night at the Opera” in the apartment when Groucho says, ‘come along kiddies you’ll be late for jail”, Harpo mimes putting on lipstick and powder, etc, they go about their zany business. They did that at home. They all know the gag.

They never laugh at their own or each others jokes. That makes it funnier