If you've ever tried to build something very big in Kerbal Space Program that can get off planet without hacking gravity, then you'll know how difficult it can be to put it all together. You need to use docking ports en masse, and potentially even build it on the ground first to make sure all the parts will actually fit together. That's not going to be necessary moving forward, as the latest version of the game (update 1.11) adds in-space construction to the game, letting Kerbals fit parts together in space.
The EVA construction tool isn't just good for helping you to build massive superstructures and ships in space, though. It's also super useful if you've forgotten to add something that you later need. Even if you've flown halfway across the solar system.
Found your solar panels don't quite orient right on your Jool mission vessel? Send a rescue mission with a spare panel to get it fixed up and bring everyone home. Not quite lined up the ladder right on your moon lander? Send a Kerbal to add one before touchdown.
This is a lifesaver feature for anyone planning larger, longer term missions, where sometimes something just gets missed off the mental checklist.
But it'll help make monster spaceships too.
