A major advantage of mass selection is:
Because mass selection avoids intensive inbreeding and retains many selected parents bulked together, resulting population preserves substantial genetic diversity and heterozygosity buffer. Broad base of alleles confers buffering against diverse environmental stresses, disease races, and climatic fluctuations, granting stable performance across years and locations. Unlike pure lines that may fail in off-type environments, mass-selected varieties contain mixture of genotypes complementary in stress tolerance, maintaining yield stability due to population buffering mechanism described by Allard.
Ref: Harlan JR. Crops and Man – landrace adaptation; Ceccarelli S. Participatory breeding for wide adaptation