I had a simple water separator for an compressor on my bugeye at first and it did an okay job.
Then i got a Greddy Catch can and it caught a lot more.
Imo, I think anyone who does any tuning should have some time of device to help reduce/eliminate the oil in the air intake. Also, the main reason I got one was b/c i bought a brand new TMIC and I wasn't about to get it coated with an oil film or have start dripping oil.
However, on stock cars that never get accelerated hard.. I would never buy one.