You only need to use the Smart Switch app on your phone if you are transferring directly from phone to new phone, I've used it and it works excellent. This is useful if your Carrier mails you a replacement phone and you have time to do a direct transfer, just make sure both phones are plugged in. You'll need Smartswitch on both phones.
If you want to back up your phone prior to going to you carriers store to do an instant swap, then download the Smartswitch program for your PC or Mac, Get it here:
Samsung Smart Switch™ (look towards the right where it says "Get Samsung Smart Switch"). When you use the Smartswitch on your PC/Mac, you do not start the smartswitch app on your phone. Just start the program on your PC/Mac, plug the phone in and that's it. By default it backs up everything, you can change that in the programs settings if you want.
I found that it restored all my call logs, SMS/MMS messages, pictures, settings, etc. The only thing that didn't transfer over for some reason were my Ring tone setting s for each app that I changed.
One thing I would suggest prior to bringing your old phone back, and this goes with all phones, Encrypt your phone first (Settings -> Lock screen and security ->Other security settings -> Encrypt phone). Tell it to Encrypt the entire phone (it will take a bit). Once it's encrypted, then you can do a factory wipe. This will prevent anyone from being able to recover any files from your phone once you hand it over. I'm in the IT field and I've been able to restore deleted items from a phone after they've been factory wiped. When they were encrypted, it's not so easy and almost nearly impossible to recover anything from it because the encryption key is discarded during the factory wipe and without it, you can't decipher the files.