I guess it it good practice to wire both the grounds and 5v signals on this type of IC, but I have made simple projects before and only connected 5v and gnd on one side of the chip, what are the potential issues with this? I guess they are internally connected so I can't really see the point in connecting them all unless you will be drawing any power through it?
Try reading the datasheet.
a) Each VCC/GND pin can only handle 200mA. You'll do damage if you only connect one power supply pin then load up the chip I/O pins.
b) The pins may
be connected internally but each VCC/GND pin feeds a different set of I/O pins. If you only connect one power pin then load up the "wrong" I/O pins then again, you'll doing damage.