I am not sure if you can do without it, but it is handy to have. If you leave master sync on and go to General - Accounts - Samsung account - touch here, you will see what it syncs. Be aware it will sync the Samsung Calendar and Samsung Contacts not Google ones, but you can merge contacts and check each contact if it has a Samsung or Google logo or both. Also go to Contacts - menu Contacts to display and check and decide if you want contacts on both.
You don't need to use your Gmail address, any other email you have will do.
Do you remember setting a Samsung account for warranty purposes.
If you have to master reset your phone, or buy a new Samsung, the 1st thing the device asks is to enter your Samsung account before your Google account.
Samsung will save specific data that Google will not, memo's , stock browser bookmarks, and other apps on Note, Tab and S5 devices.
I would have it on, you don't need to sync it very often. You can use also Kies on a computer like I do to create a full back up via usb, and transfer media. These will save separately to the cloud based Samsung account data, so account syncing is still worthwhile.
Basically if you have a Samsung, use and back up to Google sure (I don't backup media to Google personally), but having the Samsung account syncing occasionally is worthwhile. Even if you don't sync or use the Samsung Calendar or Samsung merged Contacts and leave these unchecked, the rest can be useful if you have to reset.