I don't use BGAs but have some SOIC parts I use come in sealed bags complete with the moisture detector.
I just make it a point to use them immediately after opening the bag, and reseal the bag quickly.
I also have a Zephyrtonics ZT-1 hot air bath in my shop http://www.zeph.com/bgs_airbath.htm
I do run a business and have some form of production going on ,and I'd rather take the precautions (which costs nothing or very little) rather than deal with product returns, warranty repairs, free shipping, bad PR when people talk about problems, etc.
If you're just a home tinkerer and using the completed projects for yourself, you probably have nothing to worry about but your own DIY project.