I always wash any fabric that will be washed in regular use such as a quilt. I'd rather not wash fabrics for wall hangings and maybe Christmas tree skirts. Most fabrics, especially cottons, shrink and not all shrink at the same rate. I'd rather be safe than sorry. I don't iron it before I put it away. Who knows how long it's going to be there and I don't want to iron it twice.
Fabric has sizing and it can slightly twisted when put on the bolt. Washing addresses both of these issues.