This question is best answered by reading the research published by Dr Lynette Morgan and Simon Lennard of SUNTEC, a copy of which is included on this website.
In simple terms we change large mineral crystals, which are too big for the plants plumbing system (its xylem), into tiny mineral particles that the plants can easily take up and translocate.
This is particularly true of calcium. There may also be a physical blocking of the xylem by mineral crystals which also bind up essential nutrients and prevent them getting to where they are needed. In CALCLEAR treated water the mineral particles are so small that they can easily pass through the plants tiny capillaries and simultaneously flush out any debris.
In short we just make the minerals more palatable, pack in the calcium and promoted healthy cell development.