The purpose of grinding spring ends is to distribute the force applied at the spring end across the largest possible surface area. This is typically done when the spring will be compressed between flat-end plates.
However, end grinding is one of the most expensive processes in spring manufacturing. If your assembly’s production volume is high enough, it may be more cost-effective to design components that mate with unground spring ends. This way, the load is still distributed across a large surface area without the high cost of end grinding. This is typically the case in automotive McPherson strut assemblies. Another case where grinding might be avoided is large index springs, particularly with very small wire diameter.