Comment by LegionMammal978

When you convert a generic Turing machine into a Tree Evaluation instance, you end up with square-root space with respect to the original runtime t, but the new runtime will be far, far slower. IME, with these types of circuit reductions, the runtime typically becomes exponential in the space required, which is just about 'as long as possible'.

If we're being pedantic, it's trading time for the space guarantee.