Data files half empty in SQL Server. Is that a problem?
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.