An incredible design on paper can be a disaster without adequate floor prep.
A simple renovation project can be a disaster without adequate floor prep.
A budget can go bust without considering the need for floor prep.
Patching and leveling, along with shot blasting and grinding, are common examples of slab preparation.
It can be as minimal as skimming over fine cracks, or more significant like shot blasting the substrate and pouring self-leveler.
The common point—do it and do it properly.