Declaring a ``++NUMBER++`` variable without any precision wastes memory because Oracle supports up to 38 decimal digits by default (or the maximum supported by your system, whichever is less). If you don't need that large a value, you should specify whatever matches your needs. This will save memory and provide extra integrity checking on input.
This rule also applies to some ``++NUMBER++`` subtypes as well: ``++NUMERIC++``, ``++DEC++``, and ``++DECIMAL++``.