What is the material-ui box component for?

The other answers don't really explain the motivation for using Box.

Box renders a <div> you can apply CSS styles to directly via React props, for the sake of convenience, since alternatives like separate CSS files, CSS-in-JS, or inline styles can be more typing and hassle to use.

For example, consider this component that uses JSS:

import * as React from 'react'

import { makeStyles } from '@material-ui/styles'

const useStyles = makeStyles(theme => ({
  root: {
    display: 'flex',
    flexDirection: 'column',
    alignItems: 'center',
    padding: theme.spacing(1),
  }
}))

const Example = ({children, ...props}) => {
  const classes = useStyles(props);

  return (
    <div className={classes.root}>
      {children}
    </div>
  )
}

It's much shorter to do this with Box by passing the props you want to it:

import * as React from 'react'

import Box from '@material-ui/core/Box'

const Example = ({children}) => (
  <Box display="flex" flexDirection="column" alignItems="stretch" padding={1}>
    {children}
  </Box>
)

Notice also how padding={1} is a shorthand for theme.spacing(1). Box provides various conveniences for working with Material-UI themes like this.

In larger files it can be more of a hassle to jump back and forth from the rendered elements to the styles than if the styles are right there on the element.

Cases where you wouldn't want to use Box:

• You want the enclosing component to be able to override styles by passing classes (makeStyles enables this. <Example classNames={{ root: 'alert' }} /> would work in the makeStyles example, but not the Box example.)
• You need to use nontrivial selectors (example JSS selectors: $root > li > a, $root .third-party-class-name)

A Box is just that, a box. It's an element wrapped around its content which by itself contains no styling rules nor has any default effects on the visual output. But it's a place to put styling rules as needed. It doesn't offer any real functionality, just a placeholder for controlling the styles in the hierarchical markup structure.

I often think of it as semantically similar to the JSX empty element:

<>
  Some elements here
</>

But just with some Material UI capabilities:

<Box className={classes.someStyling}>
  Some elements here
</Box>

The Box component in Material UI it has a lot of useful stuff

The most important thing is that box element has been built in with material-ui/system functionalities by default that mean you can apply system functionalities to what you need if you use it as wrapper

Like this example:

<Box bgcolor="primary.main" color="primary.contrastText" p={2}>
  primary.main
</Box>

and of cores you can add css class to it as you like or not

the other good useful thing that it offer it can be warp in other components and be very helpful to apply system functionalities to it

Like this example:

<Typography component="div" variant="body1">
  <Box color="primary.main">primary.main</Box>
</Typography>

Both of examples above i took them from documentation you can find them in this link :here

and you can find what i mean by material ui system functionalities:here

Note: you can add any of material ui system functionalities to any component like docs here but i recommend you to warp what u need with box component it make life a lot easier