There would be a huge downside in the real world.
The real world would seem dull, boring and depressing. As you cannot have that rich experience as in that virtual world.
A bit like drugs. It would create a dependence which would increase indefinitely until it would be extremely hard to live anything in the real world.
One issue with learning and training, is that you'll have the same limitations as now. You are still human, just connected to a machine and time cannot accelerate to learn faster.
However if we could move, change time to whatever place we want, create whatever we want. And still look real.
Then that would maybe make something very interesting for learning and training. It wouldn't be faster. But for example a teacher would be able to create a world where they can help the students learn better, with images, simulations, stories...
However that may also create some issues where it wouldn't be wise to recreate wars, death and other things which can be shocking for people. Because of that realism, it would be very hard to distinguish between a simulated war/death and a real one.
Tho it would maybe create a huge benefit for training for flying a plane for example. Cheap and no risks to break anything.