This might be one of those instances where "your mileage may vary" depending on the rest of your query and the size of the file(s) being accessed/created. Running some benchmarks might be in order.
I have to think there was -some- reason for this note in the doc:
Note: If your query contains a large number of COALESCE function calls, it might be more efficient to use a natural join instead. See Natural Joins.