If you feel your drive is fragmented, it's in most cases faster to format en reinstall than to actually defragment a 1 TB drive using whatever utility.
This is actually quite true. You'll be done faster doing a restore from a Time Machine backup, erasing your hard drive and re-writing your files from scratch, than the successive data reads, moves and rewrites required in a defragment operation.
That said, count me in as being in the camp that says defragmenting is no longer needed. Back before multi-hundred-gigabyte drives (let alone multi-terabyte ones), storage space was tighter and file systems were a lot less sophisticated. And at that time, contiguous space was harder to come by.
But now, this is rarely the case. The only time fragmentation may become a real problem is when your hard drive is more than 95% full... and at that point, you have two realities:
1. Defragging a 90%+ full drive that's a several hundred gigabytes or more is either not going to take very long at all (because there's no fragmentation) OR it's going to take a
VERY long time (because the fragmentation will be very high and available space will be very low).
If it's the latter, you're probably looking at multiple hours, if not days, to defragment... time you won't be able to use your Mac. It'll take definitely take longer than the time "wasted" by just leaving the drive the way it is and continuing to use it. And definitely longer than wiping and restoring from a Time Machine backup.
2. Even if you DO defrag such a drive, you're only masking the real problem here: you're running out of space and you need a bigger drive. The drive will either fragment itself again pretty quickly, OR you'll run out of space, be forced to upgrade, and all that time spent defragmenting will be wasted for nothing.
As for Macs running slow: most of the time, such problems can be traced to lack of RAM, not defragmentation. If you're paging out constantly and the hard drive is slowing you down because of it, then the problem isn't the hard drive. It's that you're out of RAM.
As for Time Machine: that's mainly a read operation on your boot disk, and a straight write operation to an external drive. If you're not meddling with your Time machine disk, nearly all of those write operations should be contiguous. Spotlight is very similar. Both resources will at worst slow you down only for a short time after the initial OS install (when the hard drive is going to be its least fragmented anyway).
Defragmenting used to have its use, back in the day (though I think even back then, people probably did it more often than was useful). But now, doing a defrag on a traditional hard drive is mostly a placebo, and a waste of time. If you insist that I'm wrong, fine. Waste your time if it makes you feel better.
But whatever you:
Do not defrag an SSD. Doing so will
absolutely have no benefit, and will actually shorten the life of the drive.
