Magento – Magento 2 : Disable Default Modules for Performance

You could increase the memory_limit to the minimum recommended 256MB. Outside of that, there's no real performance improvement to be gained in editing your htaccess.

The best htaccess is not having one at all. Move and/or rewrite your rules into your vhost definition in Apache and disable overrides.

For highest performance use AllowOverride None everywhere in your filesystem.

Source: http://httpd.apache.org/docs/current/misc/perf-tuning.html#htaccess

This really depends.

In cases you just want to hide your module output it is enough to go to Magento admin System \ Advanced \ Advanced and disable your module output there.

In case you want to disable your module completely you will need a file access but even then you may get some surprises. Some modules are almost impossible to disable completely :-)

First and easiest way is to set <active>false</active> in your module bootstrap file.

However this will not eliminate your classes if some other modules are extending them. Deleting module files is also not an option as you will still need to remove extension declarations to avoid fatal errors. Also as Petar mention in comments if your extension is implementing custom backen model or something like this and there's also some entities relying on this model deleting extension files will again result in fatal error(s).

Additionally deleting files is not removing any database entries extension created during execution of install/update scripts and/or extension's functionality.