In PoS, there will be two groups of participants like PoW.
Group A) Individuals with enough coins can run a staking masternode.
Group B) Individuals with insufficient coins to run a staking masternode, willing to delegate their stakings to a particular node. The purpose of such delegations is for nominating a master node collectively with enough stakings to acquire a masternode status, similar to how a pool can find a block with a group effort of smaller miners.