Why not? The danger is in treating a machine translation as the end product, good-to-go for humans. Using a machine for the first draft saves you some time. Put the extra time into polishing what the machine gave you. Some parts will be fine; some will be wrong in ways that a machine can't be expected to know; some will be disastrous.
Tip: Watch out for any non-English words that happen to occur in the course of your English text. (Assuming English source.) The machine doesn't know that they're in a third language-- or even in its own target language-- and will try to translate them as if they're English. This is how I ended up with the German translation of a story set in Japan involving repeated drinks of willen. (This is really true.) I have had similar interesting results translating Italian into Italian under the belief that it was English.