Some great points found in this article @ codeable:

Things break eventually. And that law applies to websites as well. More: if you’re piling up plugins, themes, and code snippets to build your WordPress website on your own, you’re going to run into issues sooner or later.

This is mainly due because there are so many elements that need to fit in as smoothly as possible you can’t be aware of them all unless you’re a developer yourself. As Daniel stresses this point even further:

If you plan to have something like a small personal blog or maybe a static business site, it’s not that critical tackling an issue as soon as it presents, unless you live off of your website. That’s a scenario you don’t want to have. For sites like eCommerce stores – but not exclusively for them – I would never recommend a client to manage it on their own. For example: when WooCommerce went from version 2.x to version 3.0 there were major changes and things just fell apart. Business owners were left with websites that people could not purchase from and that’s just not acceptable.

Even though you’re in the I-want-a-new-website mood, don’t draw a blank on how you’ll be taking care of and maintaining your future website. Especially, if you’re trying to make a living off that where your site would need to function 100% of the time.

Having an experienced developer do that for you enables you to address this concern in a cost-effective manner and makes the whole process less painful.