Generate a comprehensive 500-word article outlining strategies and tactics for automating upsells and cross-sells within a SaaS business.  The article should cover various automation methods, including email marketing sequences, in-app notifications, and website pop-ups.  Focus on the specific benefits of automation, such as increased efficiency, improved conversion rates, and higher customer lifetime value.  Include real-world examples of successful upsell and cross-sell automation campaigns. The article should also address potential challenges and best practices for avoiding a negative customer experience.  Specifically address how to segment customers effectively to target the right offers at the right time, and how to personalize the messaging to resonate with individual customer needs and preferences.  Finally, provide a checklist of key considerations for implementing an automated upsell and cross-sell strategy, including technical requirements, legal compliance, and ongoing monitoring and optimization. The target audience is SaaS business owners and marketing managers looking to improve their revenue generation strategies.