Connecting the dots between marketing and sales is hugely important -- according to Aberdeen Group, companies with strong sales and marketing alignment achieve a 20% annual growth rate, compared to a 4% decline in revenue for companies with poor alignment. If you can improve your customer's' journey through the buying cycle by using digital technologies, then it's likely to reflect positively on your business's bottom line.
In some contexts, the term SEM is used exclusively to mean pay per click advertising, particularly in the commercial advertising and marketing communities which have a vested interest in this narrow definition. Such usage excludes the wider search marketing community that is engaged in other forms of SEM such as search engine optimization and search retargeting.
Digital marketing is defined by the use of numerous digital tactics and channels to connect with customers where they spend much of their time: online. From the website itself to a business's online branding assets -- digital advertising, email marketing, online brochures, and beyond -- there's a spectrum of tactics that fall under the umbrella of "digital marketing."