Do you mean the I/O pins that are shared with other peripherals or any I/O pin.

I should have said 'dedicated I/O'

The enabled dedicated I/Os (UART, Timers, interrupts etc) start from P0.0 and continue upward in a specific sequence. If you later enable the dedicated I/O that is, say, third in the sequence all enabled dedicated I/Os with higher 'sequence numbers' move up.
Example, if you initially decide that you do not need the UART (first in sequence) and later decide that you do all other dedicated I/Os move two pins 'to the right'

Erik