Rumor has it sawdust, or wood in general, ties up nitrogen while it breaks down. Sawdust may be the worst due to the lack of airflow. That said, before I knew any better I got a ton of sawdust from a
local shop. It ended up having a lot of plastic bits and was overall a nightmare. After cleaning a bunch we did spread it on the grass as a killing barrier about four inches thick around 6feet by 10 feet. I then spread a couple bags of soil, some
straw and let it sit for a few months, then tried to plant a cover crop of buckwheat. It failed. Planted another and another, adding some compost here and there. Then a layer of
chicken coop shavings. That time the buckwheat took. Then I chopped and dropped. Ran our meat chicks over the area for a couple days. Let all the excess seeds sprout. Chopped and dropped again. This was over the past two years. At the next break in the weather strawberries are going there. I think its good now, though a layer of sawdust is still visible when I dig.
It wasn't worth it. Clean sawdust, maybe if I don't want to use spot for awhile.
Woodchips are what I love. I know, it's a thin line. So far I've had great success but this year I may have took it too far ;)