I don't pre-wash unless it's fabric that has been recycled.
Any "new" fabric i get will be starched and ironed anyway so it's not a lazy thing. It wouldn't be any more work to wash it before i starch and iron. I love the look when fabric is unwashed and then crinkles and shrinks. Now that i think of it, i could probably just starch it in the washer, spin it and iron them that way. Could even save a step???
Because i'm wetting it and applying heat, any bleed will begin to show right at the ironing stage. I've only ever had one fabric bleed enough that it worried me so i set it aside for a project with all dark fabrics.
Every time i buy something that is previously used i will wash it. I have no idea where it has been or what has been done to it. I worked in a thrift store years ago and people would literally donate bags of garbage. It was a terrible thing.