+1 Other than the safety aspect to mains cables that Barry and others have mentioned, as far as do mains cables make a diffrence, as long as the cable uses the correct guage of wire with suitable insulation material to cope with the voltage and current draw of the equipment its being used with, the correct fuse rating [if needed depending on country its likely to be used in etc ] and the correct termination of both plugs is also adered to, then in my opinion its a very subjective topic, and one i feel will go on and on, and...
Anyway; Welcome to AOS Thommy.