According to Github's documentation:
Pull requests let you tell others about changes you've pushed to a
repository on GitHub. Eleven a pull request is opened, you can discuss
and review the potential changes with collaborators and add follow-up
commits before the changes are merged into the repository.
It basically goes to say that pull requests allow you to inform other people of the changes you've made in a repository and, once open, discuss with people who collaborate in the repository about the changes that are going to be included. In addition to discussing specific commits before including them in the repository.
If you work, you only lose a little the sense of pull requests as there is no possible discussion. In any case, in a repository where you work, it would only make sense to use pull requests in the case that another person wants to add some correction to your code, but that's where that social component comes in already that is intrinsic to pull requests by definition.
If you work alone, as I say, it makes more sense to commits in a normal way, separating functionality into branches or as you like it. The idea of the tools is to facilitate the work to the people, if by using the tool you are working more than the account, something goes wrong:)
EDITO
According to fedorqui's comment, there is another case where you can (and usually) use pull requests in a repository where you work alone. This case is, as he says, when a user reports an error or a problem with the code. In this case you can solve the error and make a pull request referring to that issue , to leave the traceability of the solution.