They are cheap flowers to buy and very easy t grow and maintain. I am not good with flowers at all. I kill them most of the time. The only flowers I can grow from seed and get to survive are marigolds and nasturtiums.
There are some types of marigolds that are edible. Therefore you can grow them and add them to a salad to make it pretty. Some people also use them to make things like vinaigrette or even wine. I have yet to taste one myself.
Marigolds grow from spring to fall. They add color and beauty to your garden for until the frost finally kills them off. This also means that you are attracting bees and butterflies to your garden for three seasons with just one type of flower.
The reason I plant marigolds in my garden is that they can be used to deter many types of problematic insects like tomato hornworm, Mexican bean beetle, nematodes, thrips, whiteflies, and squash bugs.
There are many types of flowers you can grow to do the things that I have listed above. One of the more important concepts to keep in mind when setting up something like a permaculture homestead is that many things can have many different purposes. Why do many things that each only serve one function when you can do one thing that can serve many functions?