Littco
If it were not for forums like these and for information gained from other ATPL holders, how the hell would you know what to do in your hour building towards CPL?
For example we all know that for CPL level, accurate flying is a prerequisite to passing the flight test. If however no-one ever told you this and you never had read the forums here would you know that you must practice accurate flying? Although this is a minor example it shows that we need at least some structure to our hour building as we would not know or learn the skills needed without some outside input.
Personally I would like an experienced instructor to guide and set tasks and trips for me to accomplish. No matter how good I think I was at flying, I might miss out or not practice a certain skill well enough to be able to reproduce it on a regular basis. This is why a structured hour building scheme would suit me personally.
If however you have great confidence in your own flying skills and ability, and know exctly what is required of you, then there is no need for instructor input.
Personally I prefer the former.