The four specific areas that we want to mobilize in the Olympic lifts are:
Ankle
Hip
Thoracic spine
Shoulder external rotation
A lifter that doesn't spend time mobilizing these areas could have problems executing the lifts with any semblance of good technique. A lack of mobility in these areas can lead to compensatory patterns that could cause injury.
Those guys who think planks and Bosu Ball triceps kickbacks are giving their core a good workout are poor, pathetic slobs. If you really want to work the core, you've got to raise the weight over your head.