http://www.oca.org/pages/orth_chri/Q-and-A_OLD/concerningconfession.html
I wonder if the discussion there will be helpful to you.
Jumping to the bottom line, though, it is VERY "useful" -- necessary, in fact! -- to confess our sins daily to God during our private prayers. Some of the daily evening prayers are rather detailed "self-examination lists", as you already have discovered.
If you were estranged from a family member or friend, for whatever reason, you would try to "make things right" through direct communication. For example, I am extremely blessed that one of my sons -- (who is your same age, if your profile birthdate is correct) -- simply cannot even go to bed at night until he has talked through anything that he and I have argued about that day, and restored our loving relationship to what it should be, as best as he and I can manage. Similarly, a daily self-examination of my sins reminds me of how I have estranged myself that day from my absolutely "best friend", Christ. Confessing to Him through private prayer is an attempt to set things right with that most vital of relationships.
This "informal" confession becomes, then, part of preparing for my next "formal" confession through the mystery of confession. The priest is but a "witness". But he (priest) is necessary, because he has the God-bestowed task of formally restoring my relationship with God through the prayers of absolution.
So, with the "balance" that characterizes our Orthodox faith, both "ways" are needed.
I hope this doesn't sound too "mechanical" to you.
[edit] P.S. -- Such private confession would seem "useless" only if you don't believe that God listens to our prayers! We also are taught that He has forgiven us before we even get the words out of our mouths!