The cliche about successful salespeople is that they are lone wolves, closing huge accounts out of the blue, handing over the check and then riding on to the next challenge. Nothing could be further from the truth.
The best sales departments collaborate very closely with other departments, both giving and getting value in an ongoing cycle to improve the company's go-to-market strategy.
The product group obviously provides the product(s) that sales is going to sell, but on a more nuanced level it also generates the necessary product information, such as competitive comparisons and roadmaps to support sales. Sometimes sales engineering (more technical people who can have in-depth conversations with customers and give deep-dive demos) is also located in the product organization.
Marketing produces sales materials of all kinds, and, most importantly, provides leads from its various demand gen and lead gen initiatives.
Customer success takes care of customers after the purchase and is an essential source of opportunities for upsells. A seamless handover of closed customers between sales and customer success is crucial for strong onboarding and customer retention.