SegWit was submitted in August last year as part of BIP 141 (a suggestion for improvement to the Bitcoin network) and had to make the Bitcoin network much more effective.
However, despite the fact that the improvement was made a few months ago, not all developers and companies implementing it in their projects and products, including the developers of the Bitcoin Core wallet. The upcoming update (version 0.16.0) finally rectify this situation.
SegWit allows you to store more transactions in each block, leading to reduced network load, higher speed transactions and lower fees. SegWit also allows you to implement other improvements, such as Lightning Channels and payment channels, which will further increase the transaction speed.
We can say that after the introduction of SegWit in a Bitcoin wallet Core this technology will finally become mainstream. At the moment only 15% of all transactions in the Bitcoin network are conducted using SegWit. With the implementation of this technology into the main wallet of the Bitcoin network, and after it became known that Coinbase, the largest cryptocurrency exchange in the U.S., also plans to implement this technology next week, the percentage of transactions using SegWit is expected to grow exponentially.