Sprint knows when they see an excessive amount of data being used. They can't do anything about it unless you specify that your device is rooted.(Modified)
They do have specific tricks for customers with high data use. They disable the main tower where most of your data traffic comes from, but leave surrounding towers alone. That one tower will have LTE slowed but 3G will be at regular capacity. It's only done for about 2 to 3 weeks and then enabled again.
Basically, it's spot checking.
They've done it to me on 3 different occasions in 3 different areas across town. And I always check to see if it's the case by going to the next nearest tower and doing speed tests in the area.
(Just try to stay under 50GB and you'll be okay).
Sent from my SPH-L710 using XDA Premium 4 mobile app