Not clear about the function of a Buy-Sell Agreement?

From Annette Higby (of Farm Transfer & Estate Planning, published by the University of Vermont Center for Sustainable Ag), here is a good definition:

"A buy-sell agreement can be used to protect the heirs of the partners and to ensure a smooth transfer of a...partner's share in the business to the remaining partners. A buy-sell agreement provides for stable continuity of the business without a threat of termination upon the death, disability, or withdrawal of a partner. In essence, a buy-sell agreement is a provision within the partnership agreement that obligates or provides an opportunity for the surviving partners to buy...the partner's equity in the partnership."