On our team, not only is estimation worthwhile, but the process of coming to a collective team consensus on an estimate is very worthwhile. We have our product

On our team, not only is estimation worthwhile, but the process of coming to a collective team consensus on an estimate is very worthwhile. We have our product owner in the estimation session (we use planning poker), we discuss requirements, assumptions, sometimes even a potential approach or two to building a solution. That process frequently leads to discovering unknown unknowns, new requirements, and sometimes even reevaluating whether we need the change. Estimation discussions involving a big chunk of the team can be truly useful.