Today your spouse may be a healthy self-sufficient person. They may work and support themselves today. But what happens if they become disabled. Whether or not you are separated you have a legal obligation to help support your spouse and they can enforce that obligation through a Complaint for Separate Support or a Complaint for Divorce.
And if your spouse becomes disabled during your marriage (whether or not you are separated) you will likely be obligated to support them financially. Under Massachusetts law, spousal support, especially in the case of a disabled recipient can be for life.
Even if your spouse does not become disabled, if they are a candidate for spousal support (also known as alimony) the longer you are married, the longer alimony may last. Although duration of alimony is a hotly contested issue under the current law, there is a proposed alimony bill which would link duration directly (by formula) to the length of the marriage. It would be up to a Judge whether to consider your separation part of the marriage or not.
Read Reason #3: Becoming a Legal Parent