Depends on the quilt I'm going to make, and to an extent the fabric choices. I prewash if the fabrics are deeply saturated colors, batiks, hand dyes that might bleed - if the fabrics smell or feel funky- or, if they seem to have a kind of loose weave that needs to be tightened up/ might shrink a lot. I launder with a normal ccycle, regular detergent, warm water ; dry in a regular hot dryer, regular cycle. I remove the fabrics before they are completely dry and iron out the wrinkles, finish drying them. If I'm making a quilt for a child, baby, young people who may use and launder it fairly frequently I launder the finished quilt exactly how I think the new owner will. ( most often toss in washer, regular settings , wash, dry take out & use) I've found very few people will use/ enjoy a quilt if it has ( lots of hassle) care instructions included with it. If you want it to be used, loved make it to hold up. Every completed quilt I make is laundered when finished it is the final step after binding. It has not kept me from winning plenty of ribbons, awards in shows ( even 4 viewer choice/ best of show awards were laundered, washer/ dryer when finished- before entry)
The only ones I don't launder are framed wall hangings I don't expect to ever be laundered.