Just to clarify between the three different modes (source: Magento U Fundamentals course). In bold, the specific points related to your question.
Developer mode
- Static file materialization is not enabled.
- Uncaught exceptions displayed in the browser
- Exceptions thrown in error handler, not logged
- System logging in
var/report, highly detailed.
You should use the Developer mode while you are developing
customizations or extensions. The main benefit to this mode is that
error messages are visible to you. It should not be used in production
because of its impact on performance. In Developer mode, static view
files are generated every time they are requested. They are written to
the pub/static directory, but this cache is not used. This has big
performance impact, but any changes a developer makes to view files
are immediately visible.
Uncaught exceptions are displayed in the browser, rather than being
logged. An exception is thrown whenever an event subscriber cannot be
invoked.
System logging in var/report is highly detailed in this mode.
Production mode
- Deployment phase on the production system; highest performance
- Exceptions are not displayed to the user -- written to logs only.
- This mode disables static file materialization.
- The Magento docroot can have read-only permissions.
You should run Magento in Production mode once it is deployed to a
production server.
Production mode provides the highest performance in Magento 2.
The most important aspect of this mode is that errors are logged to
the file system and are never displayed to the user. In this mode,
static view files are not created on the fly when they are requested;
instead, they have to be deployed to the pub/static directory using
the command-line tool. The generated pages will contain direct links
to the deployed page resources.
Any changes to view files require running the deploy tool again.
Because the view files are deployed using the CLI tool, the web user
does to need to have write access. The Magento pub/static directory
can have read-only permissions, which is a more secure setup on a
publicly accessible server.
Default mode
- Used when no other mode is specified
- Hides exceptions from the user and writes them to log files
- Static file materialization is enabled.
- Not recommended / not optimized for production: caching impacts performance negatively.
As its name implies, Default mode is how the Magento software operates
if not other mode is specified.
In this mode, errros are logged to files in var/reports and are
never shown to a user. Static view files are materialized on the fly
and then cached.
In contrast to the developer mode, view file changes are not visible
until the generated static view files are cleared.
Default mode is not optimized for a production environment, primarily
because of the adverse performance impact of static files being
materialized on the fly rather than generating and deploying them
beforehand.
In other words, creating static files on the fly and caching them has
a greater performance impact than generating them using the static
file creation command line tool.
