I can think of below advantages of using PnP SPFx PeoplePicker control:
You can limit the people results to specific SharePoint group just by passing the group name as a property to PeoplePicker control like:
<PeoplePicker
groupName={"Team Site Owners"} // Leave this blank in case you want to filter from all users
context={this.props.context}
titleText="People Picker"
required={true}
onChange={this._getPeoplePickerItems}
principalTypes={[PrincipalType.User]}
/>
You can define which type of data you want to retrieve: User, SharePoint groups, Security groups just by passing values in principalTypes
(Multiple are possible).
PnP SPFx PeoplePicker provides out of the box required
validation (Not sure if it is available in Fluent UI - need to check)
It's always better to look at the configuration options provided by the control & match them with your requirements while deciding which one to use in your solution.