Hello my name is Dan.
A safe boot runs repair routines that do just that, repair the drive and permissions.
It will not have full functionality is safe mode.
There is a possibility that the slow down may reappear but not likely.
I find the the major cause of slowdowns are drive directories that have gotten corrupted.
This makes the finder work harder than it should have to to find what should be right there.
Consider your hard drive as a big closet that starts out with lots of room and things are easy to place and find. As more and more stuff is put in room gets harder to find so things get broken into parts and placed where they will fit and some parts get hidden and hard to find.
What is needed is everything to be located and placed into a new directory so it is easy to find.
Disk Warrior by AlSoft is what I use and recommend, it is about 90.00 at the Apple store or online.
You may not need it yet but is something to think about.