Planning Poker is a powerful estimation Agile technique used in project management
which is incredibly easy to perform in Slack with Standuply. It's used to find out how much a priority task is for a particular person.
The aim of Planning Poker is to bring everyone in your Scrum together around the table to achieve agile project management goals.
It helps them quickly come to an agreement on each task estimation with story points, days, or any other estimating unit. Sometimes teams use special poker cards, so this Scrum process looks like playing a game.
Here's a good read
with details on Planning Poker. Another one by Mike Cohn is here
As a consensus-based technique, Planning Poker involves all the Scrum team members. Every person blindly provides their task estimation according to the Fibonacci sequence (0, 1, 2, 3, 5, 8, 13, 21, 34, 55, etc). Then estimations are revealed and compared.
If all estimators selected the same value, that becomes the estimate. If not, the team discusses their estimates. The high and low estimators should especially share their reasons. Then the process runs again until all estimators provide the same estimate.
Planning Poker technique ensures there is no one person whose opinion effects on others. Everyone has their own vote and understands what is the definition of responsibility.