10 years ago (give or take), I would have agreed that a stay at home spouse is probably someone too lazy to work or not tough enough to make it. I know better now.
My best friend is a stay at home spouse. Her youngest child left for college about two years ago, and she considered going back to work. She was an orthopedic nurse (with her masters) who could likely find employment with a few courses to bring her up to date and get her license renewed. However, she and her husband decided they would be better served by her remaining home. It was very much a joint decision.
Her husband is a physician in private practice and she is now a full time doctor’s wife. She does everything not directly related to the day to day business of her husband’s practice.
[ul]She plans the office parties and business functions–everything from ordering and sending out the invitations to managing the caterers, entertainment, and location to “working the room” while the party is in process. I did event planning. It’s a heck of a lot of difficult work.[/ul]
[ul]When her husband’s business is recruiting a new employee or partner, she plans the dinners and other “meet and greets.” If that recruit takes the position and relocates, she sets them up with a realtor, shows them different neighborhoods, introduces them to various people in activities, clubs, and schools that may be of interest.[/ul]
[ul]Her husband’s business associates visit their house at least once a month for dinners, etc. She manages all the details for those get togethers and maintains the house so it’s in tip top shape and presentable should a partner stop by without notice.[/ul]
[ul]She serves on boards and committees that interest her and/or may help her husband professionally.[/ul]
[ul]She’s the one there to meet the plumber, electrician, etc. She schedules their dental, medical, etc. appointments. Likewise, she’s the one who does all the shopping and laundry, pays the bills and performs all other household chores. She makes arrangements for the few vacations they manage to take.[/ul]
[ul]Sadly, her husband’s father recently passed away. She made all the funeral arrangements (her mother in law was too distraught), got the estate in order, and spent a lot of time helping her mother in law through it. (It’s not like her husband wasn’t there for his own mother, but my friend was the one available when her mother in law would call at noon in tears not knowing what to do).[/ul]
That’s just what I can think of off hand. We don’t spend all our time discussing what she does to help her husband build his practice. 
Could her husband leave her in the lurch for some young thing? Maybe. I have a hard time imagining it because they’re so happy. However, as I mentioned earlier, she could go back to work with some effort to refresh her professional knowledge and get her license up to date.
It’s not what *I *would choose (spend all my time supporting someone else’s career? never–that’s so 1950’s), but it makes her and her husband happy. It works for them. She likes managing the house and putting together social functions. Her husband works long, grueling hours and gets to spend his scarce free time with his family or wife or playing tennis, looking through his telescope, etc. Who am I to judge their choices? They’re happy. They hurt no one.