Legal Separation is rare in Oregon. Legal Separation addresses the same issues as a divorce: spousal and child support, child custody, parenting time (visitation) and division of assests. Like a divorce, a legal separation will protect you from the finanical and legal actions of your spouse as well as provide support and stability for children. The primary difference is that after a legal separation you are still legally married and cannot remarry.
Maintaining health insurance is a major concern when getting a divorce. If this is the reason you're considering a legal separation, be careful. Legal separation and divorce typically have the same result when they are completed: a legally separated or divorced spouse usually no longer has the ability to remain on the health insurance provided by the other party's employer.
Unless you have religous objections, immigration issues or don't meet the Oregon residency requirements, there are very few reasons to legally separate instead of divorce.