You need more than one marketing channel to ensure none of your customers fall through the cracks. According to Google, combining retargeting with the other advertising you already do can help you sell 50% more stuff. In Mailchimp, you have all the tools you need to create integrated campaigns under one roof.
Drive traffic to your website with an email, Facebook ad, or Instagram ad. Then, when someone leaves without buying, you can retarget them with an ad (or, if your Shopify store is connected to Mailchimp, a product retargeting email).
Once they make a purchase and you collect their email address at checkout, send a welcome or first-purchase automation to keep them engaged with your brand.