Yep, fenders protect you, your clothing and the bike from road spray. Rain in pretty clean ; road spray is a mix of oil, diesel, rubber, dog-poo, hobo urine. Waterproof clothing will keep the spray off you but will clog up with dirt ( a skunk-stripe) and cease to be breathable.
Road spray can hang around long after it stops raining and with fenders, you don't need to keep wearing your clammy waterproof jacket in the dry.

Fenders come in traditional full-length style, bolted to metal eyelets on the frame and fork. Modern fenders are for bikes with no eyelets; they clip on or use velcro or rubber bands. They are weak, ugly and less effective.

If you have rack and fender eyelets you have the option to fit if you wish.