What does the -server option do in bitcoin node? https://en.bitcoin.it/wiki/Running_Bitcoin says 'Accept command line and JSON-RPC commands'. However I can't see any difference whatsoever. In both cases I'm able to curl my request as well as use the cli.
As stated by the help,
-server Accept command line and JSON-RPC commands
You may however also have to check if this configuration parameter has been enabled by your local configuration, usually a file called bitcoin.conf, unless configured using the -conf parameter to bitcoind.
On linux builds, this should default to
~/.bitcoin/bitcoin.conf, on Mac OS X
In this file, you can explicitly configure the server as off using the server configuration parameter.
You can alternatively pass a parameter as 1 (enabled) or 0 (disabled)
You should not be able to access your server assuming this has been toggled to 0.
The headless daemon bitcoind has the JSON-RPC API enabled by default, the GUI bitcoin-qt has it disabled by default.