I remember this really, really bothering me when I went to use UE4 and to a certain extent when I first started out with 3DSMax.
It's probably hard for people who haven't used Hammer a lot to relate, but you and I know that Hammer really does make the process of creating/placing geometry and props feel so precise that when you remove that grid, it tends to create a lot of frustration and anxiety about how things are fitting together. Anecdotally, a lot of UE stuff looks really sloppy upon close inspection, you can see it in old Bioshock games for example, that sense that things aren't really placed symmetrically or cleanly, they feel slapped together and stabbing into eachother. I would have to go back to UE4 for a bit to comment in more detail, but good Hammer work has a crispness to it that is exemplified by that precise workflow, IMO.
One thing that helped me overcome this is that 3DSMax essentially *does* have a grid, it's the coordinates on the bottom and I believe that helped me to stay grounded. Overtime I got used to aligning things more along the axis I'm working with, keeping my geo neatly along the axis functions a lot like the grid that I desperately missed. Maybe people are missing that aspect of using Max, it's something that maybe has to be sort of explained to users coming from a Hammer background.
In the long run being free from the grid is liberating, but it's something like a large grid is your "training wheels", the you move down to the 1 unit grid and feel very clever, ultimately going off the grid completely allows for so much additional freedom that you don't really want or need when you're just starting off, all it does is overwhelm and confuse. It probably doesn't help that the last time I tried to use UE4's "brush" BSP system, it was complete and utter dogshit, the worst ever system for creating simple cubes.
Anyway, feel free to leak that whole Overwatch editor anytime now...