Social Media Marketing is often set aside in most companies. How would you convince management to partake in SMM to better increase clients/customers?

For starters, companies that have embraced, improved and leveraged their Social Media presence in every industry have done 25% better than their competitors.

The key is to improve accountability of the money spent on SM activities and set measurable KPI's to ensure transparency of goals.

I wouldn't say it is left behind. Nowadays everybody are aware of power and influence which social media has. If management still doesn't understand how important it is, I would bring some good examples of companies/brand which benefited from social media, best if it would be in numbers which can't be denied.