Well....... that is really cheap, there are not further side effects ?? If not then we need to think of something as this would be a serious shortcut.?
Well, if you do it in a crucible, the only downside is the fact that it's impossible to automate.
There is a machine in Thaumcraft for automating crucible recipes, though, and if you use that the only real downside is the fact that you'll need to supply the alchemical furnaces with fuel to turn the items into essentia. It's not that much fuel, though.
Also, piping the essentia can sometimes be a bit annoying.
Alsoalso, I just remembered that you can use carrots and spider eyes instead of dye as well.