I just realized there is one more difference between following and delegated SP, than mentioned above:
In case someone follows 3 people with 10% VP each and they all vote on the same post, the old votes gets overwritten / skipped.
With delegated SP they would add up.
Good find! That'll only be true for the corner case of voting with a low strength. In any case, once you delegate, the voting % is out of your control, and that's really what is making the difference here. The net impact of SP is the same, as the low % votes also have a lower influence.
Of course, if one votes with 100%, the net effect will be the same whether you follow 3 people and get votes skipped or delegate fractions to all 3 totaling 100%.