Minifying and merging js and css can improve load times and general performance of your store, so it should be enabled in production mode, but if you have to do any kind of development then you should not enable it.
In developer mode the developer tab in admin store configuration in removed so you have to manually enter values in db to enable and disable them.
Following are the fields you need to set 0 or 1 in
core_config_data table to disable/enable these settings;
dev/js/merge_files - Merge Js
dev/js/minify_files - Minify Js
dev/css/merge_css_files - Merge css
dev/css/minify_files - Minify css
You can also choose to bundle js files, which would reduce the number of requests done to site to improve load times by setting following ;
dev/js/enable_js_bundling - Bundle Js Files
Do not forget to deploy your static content and flush cache using following commands after modifying any of these fields;
php bin/magento setup:static-content:deploy
chmod 777 -R var pub generated
php bin/magento cache:flush