It is optional. It's just opt-out instead of opt-in.

I opted out as soon as I could. I'm on unlimited so it doesn't make sense for me.

Never attribute to malice and all that... but it's rather unfortunate that they silently opted-in customers with unlimited plans who don't really get and benefits

Well, it's one way to mitigate the tragedy of the commons. You don't get much direct benefit from YOUR bandwidth use being reduced, but you do get benefit from everyone else's bandwidth use being reduced.

I hope so. T-Mobile is trying to provide their customers value that other carriers don't provide.

I very much doubt this is about 'providing value'. This gives them the general benefits of throttling users on the heaviest form of data use, with PR spun around to sound like a feature.

Binge On takes $45/month worth of data usage and gives it to me for $0 if I'm OK with throttling video to 1.5mbps. That's money in my pocket, and makes my phone more enjoyable to use. That's a feature providing huge value, not PR spin.