So what's the difference?
SegWit nested addresses can send and receive from all addresses including legacy and native SegWit addresses. While native SegWit "bc1" addresses can only send and receive from other native "bc1" and SegWit nested "3" addresses and cannot send or receive from legacy addresses.
That's half right...
Nested SegWit "3" can send/receive from anywhere
Native SegWit "bc1" can send/receive from anywhere
The issue is that some wallets and service providers (exchanges, gambling sites, webwallets etc) do not support Native "bc1" addresses at this time, so you can't send from these services to a "bc1" address... As they are likely to flag a "bc1" address as invalid and refuse to send to it.
Currently, Electrum and Bitcoin Core support "bc1" addresses.. and it seems Coinbase have started generating "bc1" change addresses... So, while uptake is slow, more and more wallets/service providers are beginning to support Native SegWit.