Importing photos filled the disk, and the originals are still on the camera

Import a card of photos and the Mac can lose far more space than the photos take, which is alarming until you know the three reasons. All three resolve on their own or with one decision.

What actually happened

1. The photos were copied into the library. Photos copies by default rather than referencing, so the originals in your import folder are now a second copy.
2. Analysis started. Faces, scenes and text recognition build an index proportional to the number of images.
3. A snapshot was taken. If Time Machine is on, the state before the import is being held.

The duplicate copy is usually the biggest

du -sh ~/Pictures/*.photoslibrary 2>/dev/null
du -sh ~/Pictures/Imports ~/Desktop/*[Ii]mport* 2>/dev/null

If the import folder still exists next to the library, you are storing everything twice. Deleting the import folder is safe once you have confirmed the photos are in the library and are not shown as missing, and that is the single largest reclaim available.

Referenced libraries, if you prefer

Photos can reference files where they sit instead of copying them, which is set in its settings before importing. It suits a workflow where the originals live on an external drive, and it means the library holds only previews and the database. The trade is that the library breaks if the drive is disconnected.

Waiting is the right answer for the rest

Analysis runs when the Mac is idle and on power, and the space it uses settles when the pass completes. Interrupting it repeatedly is what makes it expensive, as covered in why Photos keeps analysing.

If you deleted photos and nothing was freed

That is the 30 day Recently Deleted folder rather than a problem, and it applies to imports you immediately regretted. Every Apple app keeps one, and emptying it inside Photos is what releases the space.