Microsoft upgraded the disk defragmenter with Windows 10 as compared to Windows 8. The changes include better recognition of solid state drives as well as a better tuned engine to handle machines in use better.
Running the defragmenter in the background may show 10 or even 20 passes. This is due largely to writes to the disk as the machine is in use. In short, the defragmenter will continue to dynamically organize files Laptop machines may be powered down so the defragmenter may not run at a scheduled time.
Hard disks are slower so minimizing head movement has long been important to maximize performance. The vast number of sectors on a track can result in burst of data when the heads are aligned. This is one of the reasons for the increased amount of cache memory on the disk drive in addition to the faster SATA speeds.
Its a good idea to run the defragmenter and then leave the machine to complete the task overnight. This way the system disk will be tuned.
After the first time a disk is defragmented, it tends to remain that way. So when the defragmenter is run again weekly, it is fast to organize far fewer new files.
Weekly defragmentation is the default and monthly is viable for machines that are used without new software being installed daily.
Lets face it, SSD drives are nice to have but they materially add to the cost of a machine.