I understand how (and why) to add a whitespace in JSX, but I am wondering what\'s best practice or if any makes any real difference?
Wrap both elements in a
You can use the css property white-space and set it to pre-wrap to the enclosing div element.
div {
white-space: pre-wrap;
}
You don't need to insert
or wrap your extra-space with <span/>
. Just use HTML entity code for space -  
Insert regular space as HTML-entity
<form>
<div>Full name:</span> 
<span>{this.props.fullName}</span>
</form>
You can use curly braces like expression with both double quotes and single quotes for space i.e.,
{" "} or {' '}
You can also use ES6 template literals i.e.,
` <li></li>` or ` ${value}`
You can also use   like below (inside span)
<span>sample text </span>
You can also use   in dangerouslySetInnerHTML when printing html content
<div dangerouslySetInnerHTML={{__html: 'sample html text: '}} />