I already have fiberglass batts in my attic. Isn’t that good enough?
Unfortunately, fiberglass batts almost always provide inconsistent insulative properties. In other words, those areas near the center of the batts might be well insulated, but the areas near the edge (often against joists) usually aren’t. Blown cellulose, on the other hand, provides a thicker and constant layer of insulation.
We tend to use a thickness that has an R-value of 49, as opposed to fiberglass batts’ R-value of 19.