I do not understand what you mean by " I'm doing my best now to keep my o/s running smooth and as fresh as possible." That is not what file shredding if for.
#1 It is very effective if you write over with enuff data. Ones, zeros and at a random pattern with each pass. Yet the NSA can still probably recover it. If not they will make something up.
#2 Shredding a file will make it unrecoverable. Unless a lot of money is spent trying to recover it.