Here are the advantages of going with a full featured webstore package:

• Freedom to promote your brand any way you want. With your own webstore, they’ll be minimal restrictions on how you run your business, market your products, and what policies you set. There’s no marketplace rules or restrictions to tell you want to do or how to do it.
• One price for a ton of stuff. If you’re just starting out and need things like hosting, a domain name and email anyway, it may end up being a savings to get all of these things through a single webstore package rather than purchase them all individually through different services. Just make sure you comparison shop and math it out first.
• Everything consolidated in one place. Even if a webstore package works out to be a bit more expensive than getting each feature individually from different companies, you may just prefer the ease and convenience of having everything related through your business on a single invoice through a single company.
• Pre-made stores and storefronts. You could do minimal customization to one of their ready made templates and have a slick, professional looking store without having to tinker with code.
• One of the easiest options with more handholding than anywhere else. Because you’re paying out the big bucks for their service, the higher tiers of most webstore packages almost all come with a wealth of support to help walk you through the entire process from start to finish. If you’re not comfortable with some of the more technological elements of selling online, it may be well worth it to you to pay the monthly both to know you won’t need to fight with CSS and to know that customer support is available to help you whenever you get stuck.
• Synchronize with your existing marketplace. One of the best ways to ease into freedom from the big three is to start a standalone store where all or some of your items still sync back to Amazon, eBay or Etsy so you still benefit from their traffic while building up your standalone store. Many webstore packages offer item sync of some kind with Amazon and eBay being the most common. Item sync allows you to list the same items both on your old platform and in your new store but adjusts inventory accordingly as sales occur to ensure that you never accidentally sell the same item twice.