Why might it be advantageous for a large animal?

Answer 1

Two main advantages. If a herbivore, becoming so large that a predator cannot get at it. Example - no lion would dare attack an elephant. Of course if a predator also becomes large it can go after large herbivores, but at a cost of speed and concealment, so predators do not tend to become giants.

Another advantage is that if an animal does not have homeothermic blood, and they must warm up by basking in the sun, they do not cool down rapidly once they are warmed up. Some of the large dinosaurs were like this, particularly as an example the Stegosaurs, who had large plates well supplied with blood, that they used as solar panels for heat.

Answer 2

Large animals often have better access to resources like food and mates due to their size. They may also have fewer predators, as their size can act as a deterrent. Additionally, their size may help them withstand harsh environmental conditions better than smaller animals.