Nutritional grouping of lactating cows under TMR feeding systems has been discussed in the literature since the 70s. Most of the studies have concluded that using multiple, more-homogeneous TMR feeding groups is economically beneficial because of either or both nutrient cost savings or improved productivity. Nonetheless, there is not yet an absolute consensus or wide adoption. Latest studies using optimal basis for grouping and optimal diet specifications are reporting consistently greater income over feed cost ($/cow per yr) with multiple TMR groups compared with 1 TMR (3 TMR = 46 to 77 and 2 TMR = 21 to 45). Critical factors that determine the economic value of nutritional grouping are (1) basis for grouping, (2) diets’ specifications, (3) effects on milk production, and (4) additional costs. It has been strongly documented that grouping cows according to their simultaneous nutritional requirements (a.k.a., cluster grouping) is optimal. Cluster grouping is superior to other methods such as grouping by DIM, milk production, or production and BW combined. However, the dairy industry still uses less than optimal grouping bases. Using cluster grouping would enhance the positive economic impacts of multiple TMR. Next, groups diets’ specifications seem not to be optimal either. The concept of lead factors, which are only based on group average milk production are heavily used. Nonetheless, diets should be more precise following overall group nutrient requirements. Providing more precise diets will also be in favor of grouping economics. Next, an area that requires further attention is the potential negative effects of grouping on milk production because of either or both social interactions or diet concentration changes. Although the literature is inconclusive on this, latest studies indicate that multiple TMR largely outperform economically 1 TMR even after considering plausible potential milk losses of grouping. Finally, additional costs of management, labor, facilities, and equipment required for grouping are farm specific. The few studies that integrated these factors in their analyses found that multiple TMR would still be economically superior to 1 TMR.