The situation where group selection is a necessary explanation, is in order to solve the primary problem of life - which is the sustaining of life in the face of the tendency to mutational meltdown (which is the biological special case of the general phenomenon of error catastrophe).
The main problem of life is not in the initial arising of replicating entities - but in their remaining alive across generations given the intrinsic tendency of informational errors to occur and to accumulate - leading to extinction.
The problem of error in information can be diminished by better quality replication, and by repair of errors - but to do this requires relatively complex adaptations, and these must arise in a context where errors are accumulating all around.
It seems that the simplest and most reliable - and indeed, ultimately always necessary - mechanism for controlling informational errors is selection. In other words, there must be reproductive suppression (preferably elimination) of those entities which have accumulated significant informational errors - these errors must be eliminated from reproductive lineages before the information becomes so corrupted that extinction occurs.
This is the basic role of group selection. All living things need to develop networks of inter-individual communications; that is the individual entities must become a complex system. Complex systems are - by their nature - able to act to maintain and continue themselves; and the first and necessary self-perpetuation of the system is to suppress individuals with corrupt information.
In biological terms, individual entities gain deleterious mutations; and the first job in sustaining life is to eliminate individuals with deleterious mutations. This is most straightforwardly done by suppression of reproduction of mutationally damaged individuals (up to and including killing them).
This is a classic, indeed archetypal, situation of group selection. The reproductive interests of the group (that is the lineage) must prevail over the individuals - the group benefit is imposed upon the individuals - and this happens because the group has itself become an entity (i.e. the group has become a complex system) due to its relatively dense network of inter-individual communications.
So, the necessary step in the evolution of any potentially multi-generational form of life is that group selection must apply.
Absent group selection, and life will be snuffed-out by mutation accumulation and mutational meltdown almost as soon as it has arisen.
Hence, group selection is absolutely necessary to life.