Andreas Antonopoulos, internet security expert and author of O'Reilly Publishing's Mastering Bitcoin just published his thinking on Segragated Witness and what it will do to increase Bitcoin's efficiency on Medium:

Here is the TL;DR from his article:

"Segregated witness [...] has two main effects on the fees paid by bitcoin users. Firstly, segregated witness reduces the overall cost of transactions by discounting witness data and increasing the capacity of the bitcoin blockchain. Secondly, segregated witness’ discount on witness data corrects a misalignment of incentives that may have inadvertently created more bloat in the UTXO set."

Read his full article here on Medium:

https://medium.com/@aantonop/segregated-witness-and-aligning-economic-incentives-with-resource-costs-7d987b135c00

Or follow him on twitter: https://twitter.com/aantonop