I think it's great as long as they have shelter sheets blankets etc. I watch extra carefully when it's muddy so they don't slip or do anything dumb. I will also recommend fly predators for the summer so the bugs are not very bad
It's perfectly fine to leave your horse out 24/7. If it's cold and windy I would recommend a wind breaker so they are not shivering out there. If it's very hot it's good for them to stay outside but to make sure they have a water sorce at all times and some shade :)
As long as your horse can cope with the weather (winter) and have access to water, shelter and hay if the grass isn't great. I think it's great to have them out! My warmblood is out 24/7 from May to start of October and he loves it. We also have some horses on the yard who are out 24/7 and it's great for them especially the older horses really good for their bodies to have the room to move and not get as stiff.
It is better and more natural for horses to be outside. Mine are out 24/7 without rugs summer and winter with access to a feed shelter at all times. They are only rugged in winter if it is especially cold or it snows and my cob has a fly rug on in summer.
KEeping your horse in a paddock or pasture is great for them, especially energetic horses as it gives them room to be a horse and use some energy. It's more natural to them than being in a stall, but it's a personal choice :)
Much better for the horse's health and gives a much better muscling. It also prevent horses getting bad habits. I don't see any cons for having the horse outside 24/7 if it has a shelter. Especially my Icelandic horses.