Voice chat room
The owner and CEO of Discord Jason Citron has secured nearly 20 million in investment funds for Discord.
You are sharing server bandwidth with every other discord user.
Meaning if you are using discord and need voice coms for say example your guild is raiding something, and every other discord user on the planet decides to log on YOUR guilds raid is going to suffer because you don't have dedicated bandwith discords overall performance will suffer immensely.
https:// Free account have no tangible restrictions.
Premium account is just a way to say "thank you" to developers.