Sales and Marketing functions need to work extremely closely if leads are to be found and converted into paying clients or customers. Many companies will have a sales strategy as well as a marketing strategy, but they cannot be written individually as they are interdependent. A marketing strategy has to consider the business' sales goals and objectives to craft campaigns. The sales strategy has to factor in marketing projects and campaigns that could impact on activities. And of course, both have to reflect the overall business strategy.
The line between the functions is now so blurred that some companies have given up having separate departments and now have just one joint Sales and Marketing department. Yes, people may have different roles within that department, but there is a distinct cross over.