What is this for (vacuum-->transmission line?)

[botboy]

Just curious what this is. I have either a TH350 or TH400 transmission, auto, in my '72 Chevy truck. There's a length of tubing running from a vacuum port in a boss in the intake to the transmission, just curious what this is for and if I'll hurt anything by putting around the yard without it hooked up? I had a vacuum leak there apparently (at least plugging the hole fixed the rough idle problem I had) and I want to drive the truck into the garage since its damn cold out there, but don't want to hurt anything (at least till I can put a manual in its place )