All IMHO! I mention the against ideas mostly because the pro ones are so well known.
- Bipedalism might support a better view of prey in a grassland
- Human locomotion otherwise suggests a fairly open environment.
- Hands - not great for climbing trees unlike other primates.
- Non-gripping feet.
- Humans need copious amounts of salt and water.
- Human skin is ill protected against sun and heat.
- Such environments can become cold at night. Without fire this would be difficult.
- Lack of protection against predators.
- Human babies are a burden and cannot be carried easily unlike other primate offspring.