it is generally recommended that you cut 2 layers at a time- more layers you invite un-even cuts
I have many cutters with a variety of blade sizes (18mm, 27mm, 45mm & 60mm) i generally only use my 60mm if i am cutting thick/heavy fleece/minkie, heavy layers of flannel, denim, corduroy, squaring a thick/lofty quilted quilt.
some people use their 60 for regular cottons- but it is generally easier to use the 45.