To pre-wash or don't pre-wash fabric before quilting is a hot topic. There is much discussion around this subject but it's pretty much a personal decision.
Reasons To Pre-wash Your Fabrics.
1. To prevent fabric bleeding/ running.
For some types of fabrics you may end up sorry if you don't wash them. Batiks, for example, contain a lot of excess dye. Fabrics with a lot of red, dark blues, purples is very likely the colors will bleed. Why take the chance of bleeding fabrics cost does not determine colorfastness.
Recommended products for you to use:
Color Catcher Helps prevent dye transfer and color runs to maintain original colors of clothes.
Note: Do not wash small precuts, like jelly rolls and layer cakes, because you might end up with a pile of twisted threads.
Fabrics tend to shrink a lot , like flannel. Prewashing helps get the odd wrinkles and helps straighten the grain of the fabric. If you do prewash, be sure to prewash ALL fabric going into the piece, not just some, to avoid uneven shrinkages.
3. Remove Chemicals
Washing removes that store smell and the sharp center crease. It also gets out any chemicals used on the fabric. There are some fabrics that are not allergen free and some have formaldehyde that may be unhealthy. You don't want those chemicals onto your skin and into your respiratory system.
4. Removes Fabric Lints
Another reason to pre-wash is to reduce some of the lint. You don’t want your sewing machine to get incredibly linty. You won’t want to be breathing that in either!
Reasons To NOT Pre-wash Your Fabrics.
1. Takes Too Much Time
Some quilters don't like to prewash as it takes too much time. They just want to finish the quilt and wash it after it is completed. But if you are making a quilt that is going to be a wall hanging and never see water then don't bother washing.
If you want your fabrics to have that vintage, puckered look then don't wash them.
Sizing chemicals adds crispness to the fabric and reduces wrinkles which makes the fabric stiff for easy cutting and sewing.
This subject of pre-washing fabrics is always debated but there is no right or wrong. You will have to decide what is best for you.