Difference between Bootstrap on local repository vs. using external link

I am new to webpage development and I want to know if there is any difference (security-wise, performance-wise) between downloading a Bootstrap package and referencing it on the local repository, and not downloading the package and referencing it as external link, that is for example using this line of code:

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"></script>

I know there are dependencies managers such as Composer etc., but they seem really difficult to handle and I find it easier to just reference the package as an external link.

Thank you