As far as I know, some legal definitions of shareholder majority are expressed in terms of "50% of the shares plus 1 share". Why not simply "more than 50%" or perhaps "an amount of full shares that exceed 50%"?
In an extreme example, let's say a company only issued five shares and these shares are only traded as one piece (no fractional shares). Then 50% of five is two and a half, plus one is three and a half, but with only full shares available I need four shares to achieve that. So in this case I need to actually own 80% when one share less would already be 60%. Of course this effect gets smaller the larger the total number of shares is, but the question remains: What is the rationale behind this strange regulation and formulation?