MSP430G2553 and LDO ADP162: Is an external pull-down necessary?
If cost is not an issue, and power consumption not critical, I would put a 10K or 100K pull-down on that line. It will enforce state before the MSP VCC is high enough to guarantee state, and while / if the MSP is in reset, it will guarantee state as well. Invert this to a pull-up if the desired state during reset / boot-up is for the device to be "on".

Without this pull-down (or pull-up), you might see odd 'Heisenbug' behavior in the lab -- sometimes the local humidity and temperature conditions can cause unexplained inconsistent behaviors. This can also commonly happen on SPI or JTAG lines where a pull-up is omitted.

If you aren't building a million of these, the cost of adding the resistor is low (layout impact, assembly cost impact, the actual cost of resistor is negligible). If it's not a low-power wearable type application, a 10K resistor at 3.3V will cause you to burn an extra 330uA of current; 33uA if you use 100K.

In general, I would suggest that for I/O lines that control "actuators" / state / other items, something should enforce the state on that line prior to the system coming online and taking active control. With a properly partitioned system design, you could spend the pull-up/pull-down only where needed (i.e., a LDO control line), and leave other I/O floating, since those I/O have no effect until the LDO is powered on.