In DOL starter full line voltage is fed to motor which will 
start motor with a shock, it also  draws very high current 
than rated current(around 6 times), but if we use star-
delta starter , the motor starts as a star connection later 
which is converted in to delta.
using star connection the line voltage is devided in two 
phase voltages, also impedence is also increased due to two 
star windings which result in low starting current and low 
torque which will prevent motor to run with shock.
another difference is DOL starting takes less time while 
star-delta takes more time to run at rated speed.