I have a multiple TB database and I have been doing some clean-up and dropped many tables. So now the data files are half empty. If I don't care about releasing the space to the operating system, is there any other reason to shrink the files? I am thinking that now at least I do not need to worry about auto-growth settings, which might slow things down if I add a large table with ETL.
No. Unless you need the space for something else it is not a problem at all. The unused space won't cause any extra CPU or memory use, empty pages won't consume space in backups, etc... As data grows in future it will use the empty allocated space instead of requesting more from the filesystem.
In fact shrinking can cause issues such as extra fragmentation, that you may end up spending time rebuilding indexes to resolve, so should be avoided unless needed.