MobileSync directory getting very large, why?

So I have been using my iPhone 7 since it came last year. Been backing up via iTunes. The folder is now 336GB!!! The iPhone is the 256GB model.

I needed to do a full restore and I didn't have enough space on my HDD to do the restore. iTunes kept complaining. I guess iTunes needs some "scratch" space to do the restore. Fine. So I moved the entire MobileSync directory to an external drive and did the symbolic link trick to point to the new location in order to do the restore. Big pain in the butt but it worked. Luckily I had a 4TB external drive handy.

After I successfully restored my phone, I restored the symbolic link to the original location on my laptop HDD and decided to do a brand new backup. Since the MobileSync directory was empty (I did not move the old backups into the original location), iTunes thought I had never backed up my iPhone before and I was able to do a clean backup. This backup folder (when done) was only 113GB.

Why was the original MobileSync folder so bloated? As far as I could tell, when doing the restore, there was only 1 backup in the MobileSync folder (I only had one choice for a backup to use in the restore step). Is this normal? This is the first time I have had to do a restore, but do backups religiously for just such an emergency. I know with my PC backups, the backup software saves several versions so I fully understand why a 1TB drive could result in a backup that is several TBs. But I guess I don't understand why Apple does this for the iPhone, especially since I did not have an option to back up from various backup files.

Should I just "purge" my MobileSync backups every 6 months or so, and do a fresh backup to minimize the wasted space on my laptop HDD?

Thanks for any help or suggestions.