Reference : StackOverflow[https://stackoverflow.com/questions/42037828/odoo-10-developer-mode-and-developer-mode-with-assets]

Debug mode (most of the time used by Administrator) With this mode you can unable some advance features/options in odoo. so if you open odoo with debug mode you will see some extra menus, extra fields to more advance configuration.

Debug with assets mode (most of the time used by developers) It enables all features from normal debug plus some extra. Odoo internally use assets bundles to improve performance which internal merge+minifies all static assets like css and JavaScript. So debug with assets will use actual css and javascript files instead of minifying/merging css and js files. This mode will reduce performance but it will give you proper error message in console if you are doing some JavaScript changes in odoo

You can use this chrome plugin to quick switch between all those modes https://chrome.google.com/webstore/detail/odoo-debug/hmdmhilocobgohohpdpolmibjklfgkbi