Some ideas about the effect of appropriately selecting the size of the connections conveyed by multi-rate flexgrid optical networks are discussed. The main focus is on illustrating the relation between spectrum consumption and effective carried traffic. It is demonstrated that by introducing some order in the spectrum use, so limiting the network flexibility, its global performance is notably improved. The main contribution consists in demonstrating that using single sized lightpaths, the network throughput at any given blocking probability value increases compared to the multi-rate case. This conclusion is supported by extensive simulations under dynamic traffic conditions, considering different network topologies and traffic profiles.