Let me answer this question in two parts…
Yes, a custom email design/template can improve the conversion for your business.
The idea is quite simple. Your business is unique. And so are your needs, requirements, and goals. To that, you have a unique target audience – whose preference and expectations are unique as well.
So, your email design should be customized per these unique facets. If your audience is well-read, maybe including more texts in your email is a good option. If you’re targeting millennials who aren’t too much into reading, maybe putting up heavy graphics will bring you better results.
Similarly, if you just sell one or two products, customizing the template that highlights one or two products makes sense. If you sell multiple products, you’ve got to tweak the templates to ideally showcase all the relevant products.
Meaning to say, you cannot simply pick a ready-to-use email design/template and use it. It might convert – but it won’t convert optimally. Personalizing the template per the unique needs and requirements in your case can drive you much better results.
In short, custom email design/template does convert better, which, per your question, can help grow your business relatively faster.
NOW THE SECOND PART OF THE ANSWER…
Using fancy email templates – or customizing your template in a fancy way – is a very, very bad idea today.
In fact, the founder of Convert Kit says “Beautiful email templates are bad for business”.