When my exH left he initially suggested a 50/50 arrangement, but I instantly felt that was completely wrong. I was a SAHM for 10 years, had started working in a term time job, all to be there for my DSs, especially DS2 who has SN. I have always been the main carer and often the only one to attend hospital appointments, dentist, doctors, parents' evenings, statement reviews, etc etc.
But, exH was a very hands on father when he was home. Did his fair share of nappies, night waking, bath times and bed time reading, playing board games etc, etc.
One of his (midlife crisis) reasons for leaving, as well as his affair, was that life as my husband and a father was boring, full of routine and responsibilities, however. He dropped his request to have 50/50 care as soon as I objected and is very happy with his EOWs. It gives him the opportunity to be a good father for a few days and still have a life as part of a childless couple for the majority of the time, with weekend breaks, entertaining and socialising and plenty of holidays.
He pays me the minimum CSA formula, which I can live on and keep my term time job. I have a sneaking suspicion that his request for 50/50 was more to look caring to his OW and to avoid having to pay maintenance. She left her husband a few months before he left me and has this arrangement for her DS.
In retrospect, some of my feelings of wanting to have the boys live with me were selfish. My exH had left and taken my old life away. I couldn't bear the thought of his taking the boys away as well. It has worked out, though.
50/50 is often stated as being best for the children, but I'm not sure it is. Weekly disruption, living out of a suitcase with nowhere to call home. Having to be super organised with school work, games kits, cooking ingredients, scout uniforms, swimming kits, or having to have two of everything. 50/50 seems to be more a case of what's fair for the parents, not what's best for the children.
Then you get to when the DC become teenagers who can choose who they live with and often seem to choose the parent who has more materially or is less strict. Teenagers can be mercenary buggers.