Join Separate paths
If you have lots of separate, exploded lines (say from DWG/DXF import, then you should be able to use an alternative of Ctrl+J to join them back together without them trying to join end to end.
That is to say, if paths are adjacent to each other they are joined. But the ends of non adjacent paths aren't then closed up as well. Really basic idea, but somehow overlooked.
Sure, it's easy to Ctrl+J a few disparate, exploded paths. But for 20+, 50+, it's a joke.
There are several ways we can achieve this now in Illustrator:
1. Using custom scripts, like Join Reasonably
2. Using VectorFirstAid plugin from AstuteGraphics
Sure it does not mean it should not be in Illustrator by default, on the contrary!