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In a way it is beneficial if you want to test out new builds, champions, or play style.
I'm a slightly below average player who heavily played coop vs AI when I first started LoL.
From 1-15 I played Coop vs AI extensively. In turn this gave me some bad habits that still linger around when I play PvP, many of my examples have already been used in previous replies. I agree with many others here and my point is that PvP will make you better at PvP. Hopefully this additional reply has convinced you if you aren't already.