Hello Ohassairi,
the command is probably still available for back compatibiilty purposes.
In the unlikely case that you need to mix old devices and new devices you have a chance to make new devices behave as the old ones.
However, since IOS 12.0 the ip classless is the default and so it has been in the last 12-13 years!
In addition RIPv1 and IGRP the only classful routing protocols are obsolete.
Hope to help
Giuseppe