It also doubles your likelihood of having at least one working generator in the presence of failures. Depending on how many of your loads are critical, it might be a better bet to have two in parallel. Best case you can run more, worst case you can run the essentials just like now. Also it might be a cheaper upgrade path. Instead of throwing away or reselling the existing smaller generator to buy a larger one, just add another of the same thing you already have to your system. Finally, you could have three smaller generators and get N+1 redundancy for cheaper than two larger generators.