so you can select engis click on transport and then hold shift and let say build MEXes on another side of map and after engies are picked you will transport them on another side, drop them and they will automaticly build MEXes
but I kinda missing option to pause transport, becouse when I click on him, he immediately start picking engies, you can send him away but how far not to waste time?
and this pause would solve this, so you click on paused transport to pick units, but he is paused so he won't move until he is unpaused( when you give him direct move order he will move of course)
I found it few days ago and I love it ( thx sniping Tokyto )