A garment made from all acrylic is very warm, but it does not have the capacity to "breathe" as natural fibers do. Acrylic is often a component of baby yarns, for warmth and washability. While you can usually machine wash an acrylic yarn, they are very heat sensitive and may need to be laid flat to dry. Check your yarn label.
Depending on how they are spun, acrylics can pill, just as natural fibers can. As always, matching the project with the right yarn for the purpose is important.
When acrylic is blended with a natural fiber yarn, it may be susceptible to moths. Use mothballs to protect yarn, fiber and garments. If you don't like the odor, periodically place the yarn or garment in a plastic bag in the freezer for 48 hours to kill moth larvae. You should also air out stored fibers in the sun every now and then.