I have recently had an issue where I have been unable to install the WP Smush Pro plugin because I don't have the Manual Install or One-Click Installation options available.
I came across this post which suggested tweaking the settings in
wp-config.php. I added the settings suggested, however the one that seems to be the most important is:
What I would like to know is what real concerns should I have around setting
direct? Are there any other alternatives to installing the plugin?
This is what the official documentation has to say:
FS_METHOD forces the filesystem method. It should only be "direct", "ssh2", "ftpext", or "ftpsockets". Generally, you should only change this if you are experiencing update problems. If you change it and it doesn't help, change it back/remove it. Under most circumstances, setting it to 'ftpsockets' will work if the automatically chosen method does not.
(Primary Preference) "direct" forces it to use Direct File I/O requests from within PHP, this is fraught with opening up security issues on poorly configured hosts, This is chosen automatically when appropriate.