In our experience, if you keep keets in the coop or pen where you want them to roost at night for the first 12 weeks of life, then they will always roost there. If you bring in adult guineas, then it is necessary to keep them locked up in a coop for 4 to 6 weeks before letting them free range. Once they get used to their new home and know where the food and water supply is then they should return to that each evening.
Guineas eat bugs all day long. We got the guineas to help with the bugs in the garden. Because they can fly they tend to wander around during the day wherever they please. We do not have ants or ticks in our yard. It is hard to find any crawling bug in our yard because the guineas are very good at finding them. Guineas love termites and eat them up every year when they swarm out of an old tree. They eat bees and moths too, so you need to be careful if you have a bee hive. Guineas also like to eat the seeds on the tall grasses and weeds.
Guinea is also one of our favorite meats. Yes, we like them better than chicken!
One thing to consider if you are thinking of getting guineas and you have chickens. Some male guineas can be aggressive towards your rooster and chase him until he passes out and dies. They do not fight. The male guinea will simply run the rooster. Out of all of our guineas we have had over the years we have had one male that was aggressive toward our rooster. We do not keep aggressive guineas nor do we knowingly sell them (they end up being dinner).
Keets require non-medicated feed. They do well on non-medicated chick starter/grower or non-medicated flock raiser. Our keets eat non-medicated chick starter grower for the first 16 weeks of life, then they eat non-medicated chicken layer. The feed is a supplement to the bugs and seeds they eat where they free range.