William Blake is generally classified as a Romantic poet, but even his fellow Romantics, if they had heard of him at all (as, for instance, Wordsworth had) tended to regard him as unbalanced at best, insane at worst. Blake's views changed as he grew older, but they were always eclectic, visionary, and deeply unsettling. Perhaps the best place to look for a distillation of his philosophy is that great tirade of a poem "Auguries of Innocence," which begins with the following lines:
To see a World in a Grain of Sand
And a Heaven in a Wild Flower
Hold Infinity in the palm of your hand
And Eternity in an hour.
This opening is often quoted, but the bulk of the poem is a bitter litany of injustice and oppression.
As for what might be gained by seeing the world as Blake did, he was certainly alive to the beauty and wonder of existence. He cannot often have been bored. Blake also saw and fiercely felt how unjust the world is and how oppressed many of its creatures are. This is an excellent state of mind for an activist and reformer.
What might be lost? Peace of mind is one thing. If Blake was never bored, he was never relaxed either. Another great loss is a sense of community. For instance, Blake was a religious party of one and probably a political party of one as well. It is precisely because he was so individual and had so little in common with others that even a nonconformist like Wordsworth thought he was mad. To see the world as Blake did means always to be lonely.