Designing Your Hero. From the SG-City Forum post by Creslin (The Stat Monkey)
"Why should I spend time picking stats so long before I even max out?"
Unlike other games, it is rather easy to accumulate all the stat points you can get in SG. Once you hit that cap your stats will define the potential of your character and you won't be able to change them unless you order a Stat Reset, which incurs some penalties, or if you reincarnate, an event which happens only every 3 months and resets your character entirely. (As in back to level 1).
Therefore an early plan is a great way to ensure at least some degree of success.
Furthermore, a few other reasons to pick ahead of time would be so you can get used to your most important task very early, (killing, or POCcing) so you can choose the right units right from the start, and so you can pump tactics to the level you need to have your units sets set up properly.