Any digital strategy should be fueled by data and insight from an abundance of sources; unless you know what's happening on your website, you don't know how to make it better and you don't know what parts of your marketing are working best.
If you're spending money on any form of marketing you want to know it's working, right? An analytics package that has been set up properly can tell you where your website traffic is coming from, what it's doing on your website and, most importantly, how your customers are spending their money. Once you know which of your marketing channels are working best for you (and which aren't), you know where to invest more cash.