Two aspects to this, education and daycare. I never had any paid daycare for my children as I was a SAHM when they were little (long ago). We are, however, fortunate to have a brilliant nursery school near us, run by our LEA, so providing free education from the age of 3. Both our children started there at 3, doing 5 mornings a week (others did 5 afternoons a week). In the last term they did a full school day. Transition to reception was a lot easier as a result, and it gave me a break (much welcomed), but that wasn't the main benefit.
The school was staffed by Early Years trained specialists - teachers and nursery nurses, with some additional help from lunchtime supervisors who were older women whose own children had attended the school in earlier years. The education provided there was second to none. The school was well equipped and extremely well run. Everything they did was geared to the stage of child development of 3 and 4 year olds.
They read to the children, made books with them and helped them develop hand-eye co-ordination by drawing, painting, sewing, weaving, cooking, using woodworking tools etc, all heavily supervised. All excellent preparation for learning to read and write later, far better than drilling children in phonics before they're ready for that kind of thing. The children had a free choice which activities to do but the staff were watching very carefully and any child who consistently ignored some activities would eventually be sensitively encouraged to have a go.
The best example I remember of that was in my son's final term there, which was the summer term. The school had bought some tanks and butterfly eggs and for weeks the staff were showing the children what was happening to the eggs as they hatched, turned into caterpillars etc. Eventually they metamorphosed into butterflies. They were kept in the tank for a few hours before being released. The staff were inviting each child to spend a few minutes by the tank drawing the butterflies before they were set free. It took some persuasion, but finally they persuaded my son to have a go. I still have the drawings he produced somewhere. They were beautiful. No coercion involved. I watched the staff with the children many times and marvelled at their patience and skill.
My children had a chance to try out activities there that we couldn't have provided at home. They made friends with children from a wide range of backgrounds. They spent hours every day out in the fresh air running around, which they wouldn't necessarily have done otherwise, as I had things to do at home. They were safe and being expertly looked after and taught, and it was free! I can't imagine why anybody would down the opportunity for their child to attend a place like this. (Sadly, I know not all Early Years settings are as good as this one. It would make a difference to our society if they were.)