Custom sysctl settings - where?

In most guides (including in the firewall guide on this site) it is recommended to add any custom sysctl settings to /etc/sysctl.conf. However, it seems that such settings could also be added to /etc/sysctl.d/local.conf (or any *.conf file in that directory). Both files are included in the backup file list by default.

Are there any downsides to using the local.conf file instead of the main sysctl.conf since the latter seems to be the recommended method? I think perhaps it is a bit cleaner to use the local.conf, as that file would then only contain the added user settings.

Perhaps this is a dumb question, but I'm asking it anyway, as I don't know the answer.