Of course, you could do neither of these things and simply let the drive do its stuff. It's up to you. :)
With more spare area, write amplification is lower. The controller has more room and thus flexibility with running its defragmentation and garbage collection algorithms. The dreaded read-modify-write scenario is triggered less frequently as there's less space pressure thanks to additional spare area. If you're testing in a full-drive scenario, there's simply less data to keep track of when you've got more NAND set aside as spare area. This keeps internal data structure footprints smaller by default, which also improves performance.
It's because of this relationship between write amplification and spare area that we've always recommended setting aside 10-20% of your SSD and not filling it up entirely. Most modern controllers will do just fine if you partition the drive and leave the last 10-20% untouched.