Ooh nice tank! I was about to plant my aquarium after it cycled, but then I read this thread. So what exactly is so bad about planting with water inside?
It's just very difficult based on tank size and tools available. If it's a large tank that you can stick your arm in without it spilling over and you have deep enough substrate to just stick it in and it'll stay, then you should be good. But in a very small setup you need to use forceps and it's difficult to navigate and get things anchored and positioned where you want them.