AutoMapper .AfterMap() vs .ForMember()

Question

I was facing an issue where I could use the .AfterMap() method or the .ForMember() method from AutoMapper. I was researching a little bit but did not find any information about it. What is the difference between them or when would you use one over the other?

AfterMap:

.AfterMap((src, dest) => dest.SomeDestinationProperty = src.SomeSourceProperty);

ForMember:

.ForMember(
    dest => dest.SomeDestinationProperty,
    opt => opt.MapFrom(src => src.SomeSourceProperty)
);