Legel separation is usually pursued when the parties want to stay married for religious reasons, want the advantage of deductibility of spousal support payments for income tax reasons, want to maintain various insurance coverage's, or are do not want to wait the state statutory waiting period for termination of marital status. For some people, a legel separation is desired to set the parameters for dealing with one another while living separate and apart (especially with respect to continuing support obligations and child sharing issues) while maintaining the status of being married, and leaving the door open for a reunion/resumption of marriage.
Legel separation is not a prerequisite to divorce (dissolution of marriage).