Checkout is always the last part of the shopping experience of customers, therefore its design should encourage them to finish their purchase. However, some limits of the current version of Magento may put people off the last step. 
Let's imagine the process of filling out the checkout forms in several pages and getting back/ forward to each one when you suddenly find that you entered the wrong information. That can be frustrating, right? Besides that, the layout and design can be boring at times, too.
When you are shopping in a foreigner's store and find out that their do not display any currency rather than their base one, do you think it is inconvenient? Plus, they might let you see but do not let you make payments with your preferred currency. 
Do you feel like adding some more notes for the seller sometimes but they do not provide you with those fields like preferred delivery date/time or comment for shipping?
Here are some Magento 2 extensions that I would like to recommend to you for fixing those inconveniences for you to optimize the checkout process and increase sales. 
Magento 2 One Step Checkout - BSS Commerce
Magento 2 Checkout with Display Currency - BSS Commerce
Magento 2 Checkout Custom Fields. - BSS Commerce
Smart One Step Checkout- Aheadworks
Checkout Fields Manager - Aitoc
Custom Cart & Checkout Messages - FMEextensions
One Step Checkout Pro - Mageworld