I was in this position, where there was no financial need to work when youngest started school. ExDH had a very demanding, well paid job which necessitated regular travel away from home, sometimes for several days at a time so I knew all school runs, holidays, sick days etc... would be mine to cover as I could never hope to earn anywhere near what he was earning. Because of the hours he worked I also knew that realistically all home admin, appointments, housework, cooking etc... would be down to me. He did absolutely pull his weight at weekends but his work often took up weekend time too. Me going back to work seemed like it would be almost impossible from a practical point of view and neither of us were sure we wanted the extra hassle.
In the end however I couldn't fight the yearning to do something else so I made the decision to go back part time, two days a week, then rising to three. I did it as I wanted something for myself apart from being a mother and homemaker - entirely my choice and and I know not everyone feels the same. Until I went back I hadn't realised how much my confidence in myself had been eroded. I took a very basic low paid job to begin with as it promised flexibility but I soon realised that actually I was capable of a lot more and that once I had a routine in place working around the DCs schedule wasn't actually too difficult most of the time.
After I'd been working for about 3 years ExDH suddenly lost his job under awful circumstances meaning that I became the sole breadwinner for several years. As I was already in a job it was relatively simple to go up to full time hours and in effect we reversed roles.
Further down the line we separated and divorced (different set of reasons I don't want to go into). I am so glad now that I went back to work when I did as by the time we needed to rely on my salary, rather than just using it for treats, I was earning considerably more than I thought I could and following the divorce it meant that I was already financially independant and had pension provision etc... already in place.
I know my circumstances are probably the exception rather than the rule but I guess I'm trying to say, you never know what the future might hold and actually when you try something out it's not always as hard as it looks.