The passengers already know where they are going and they know what the weather is and will be there when they get there. Unless there is something that they should be prepared for such as moderate or worse turbulence soon after take-off, I don't bother with a PA. The people have been yelled by PAs non-stop since the first set foot in the terminal and don't need a useless PA from pilots to add to the noise clutter in airports and airplanes.