A dust cover might be adequate (or not) keeping dust off the platter and plinth. It serves little useful purpose otherwise. It does nothing to help the life of a cartridge. The latter part falls under keeping your records and stylus clean.
I have a Clearaudio Innovation with two 12" Universal tonearms. There's not even a reasonable possibility of enclosing that in a dustcover. I use a goat hair cosmetic brush to dust off the POM platter, plinth and tonearms now and then, but that's all more for cosmetic satisfaction than functional worth. I clean my records and I clean my stylii with the proper tools.