Adequate Sprint Planning is actually done by all the team members. It is not reasonable for the team representative to commit the work across the team.
Key Points for Sprint Planning
Using the prioritized backlog, the PO presents the highest value stories to the team in order. The purpose is that everyone on the team fully understands the intent of the story and specific acceptance criteria for that story. It is also helpful to explain the definition of done for all the user stories.
Every sprint starts with a Sprint Planning Session, which includes two sessions - the WHAT-meeting and the HOW-meeting. In the WHAT-meeting the team picks the User stories from the Scrum backlog, on which they will be working. And, in the HOW-meeting, the User stories picked are further broken into small tasks with a set priority and story points.
Scrum meeting representative will show the high level vision of the project. The Product Owner identifies the goal of the Sprint and justify that how it will deliver value to the product.
Before the sprint planning meeting Product owner will rearrange the user stories and give the priority to the stories.
During Sprint Planning, PO presents the highest-priority user stories to the team. Stakeholders will give feedback on the user stories. Stories may change on the basis of stakeholder feedback.
During the second half of the planning, team decide how to get work done.
PO reviews the highest priority stories with team and decides how much they can do in each sprint. Everyone should commit his or her work in this planning. If someone can't commit, the PO and team need to work together to change the shape of the sprint until everyone can commit. Sprint planning is a key collaborative effort in scrum.
Once the team has committed to user stories, the Product Owner revisits the Release Plan mapping of user stories into Sprints. With the current information, stories that the team completed in the previous Sprint, stories taken off the Product Backlog for the current Sprint, the Product Owner updates the release plan.
Scrum takes the commitment step very seriously. Each person's commitment is very important to achieve your sprint goal. Starts from reviewing sprint goals to updating the release plans, each step must be should followed carefully.