lulu - I cant reply for Markos but I find it handy to have the troops as I don't need to think which adv can I play next but which adv do I want to play next as I pretty much have any troops required even after doing the hardest FairyTale and messing up on losing a few ES along the way.
It also means that when I fail a block or 3 it again doesn't set me back as I generally have around 1k of the higher level troops available for just such an occasion ;-)