DOL is the simplest and most cost-efficient method of starting a motor but actually involve the biggest increment in the starting current, it can be many times higher than the rated currents of motor and switchgear and correspondingly places the latter under thermal loading.
If we consider that most of the supply networks may have variations based on the standard regulations up to (+) or (-) 10%, most of the equipments are made to handle these voltage variations and the operation performances not to be affected too much. In this hypothesis come the electric motors where another 10% voltage drop during startup should allow a successful start. It is well known that once the starting torque has been reached, the current drops sharply to the value of nominal current and the terminals voltage increase. But just as well should kept in mind that the torque varies with the square of the voltage being possible the mechanical torque developed at the shaft to be less than resistant having irreversible effects at startup.
A very small voltage drop (roughly 3-5%) means over sizing the power supply which is not economical since the start is successful and the other loads in the system are not affected by voltage dips.