Flex-Basis and flex-Grow together

Question

What is the behavior of a flex item with flex-Basis: 300px and flex-Grow: 1 inside a 600px container??? I see no use for flex-Basis in this scenario. Something happens??

<style>
 .container {
     display: flex;
     width: 600px;
}
.item {
     flex-grow: 1;
     flex-basis: 300px;
}
</style>
<div class="container">
   <div class="item">
   flex-item aqui
   </div>
</div>