Say you want to restrict the amount of used space on disk for Transaction log and/or Tablespace.
There's the option "autoextended" on MySQL and a lot of other commercial DBRMS MS-SQL, Oracle and so on. That's for automatic growing the objects on the File Systems. But we can also put a static value so we have to change it if there is need for.
On PostgreSQL do we have to use the quota's of the Operating System or what do we have to do for restricting the used disk space.