Act! users have some unique choices compared to other CRMs, the main one being deployment options - online, on-premise, or both. Each has its own advantages and disadvantages, and here is a brief comparison of the main features of each option:

• Cost: On-premise usually requires a high initial investment for purchasing the software, hardware, and installation, as well as infrastructure maintenance. Online Act! has a lower upfront cost, lower maintenance fees due to reduced compatibility and software overhead issues, and a lower subscription fee that varies depending on the number of users and features.
• Security: On-premise Act! gives you full control over your data security, but also requires you to maintain and update your own security measures. Online Act! relies on the cloud provider’s security protocols, which are often robust and reliable, but "theoretically" can expose your data to potential breaches or outages. The truth is online infrastructure maintenance is far more rigorous and professionally administered than on-premise setups, so more vulnerabilities tend to exist with on-premise self-hosted deployments.
• Scalability: A self-hosted on-premise Act! may limit your scalability, as you need to invest in more infrastructure and resources as your business grows. For instance, your database may grow to require SQL Server over SQL Express, and that can add significantly to self-hosted costs. Online CRM offers more flexibility and scalability, as you can easily adjust your resources and features according to your changing needs, and they already deploy SQL Server from the start.
• Maintenance: Version upgrades with online Act! are handled by the hosting provider free of charge, and often without the users even noticing. Upgrades to a self-hosted on-premise environment can be disruptive and time-consuming as upgrades have to be completed after-hours, and must be coordinated with all remote users - which is not always possible. Moreover, version upgrades with on-premise have a much greater likelihood of requiring add-on upgrades, whereas Web add-ons normally mostly connect with the data, and not the program, and require fewer changes.
• Customization: On-premise Act! allows you to customize your system according to your specific requirements, as you have access to the source code and configuration. Online CRM may offer less customization options, as you have to adhere to the cloud provider’s standards and limitations. 
• Add-ons: This is an area where on-premise Act! users have a huge advantage. Act! has a rich and mature add-on market with a wide variety of products, but the overwhelming majority are developed for the on-premise version of Act!. These include industry verticals, admin utilities, accounting integrations, plugins, you name it. And while Keystroke has developed many API add-ons in recent years, including Linktivity.net,  Act4mail, QuickMeets & QuickTasks, as well as Handheld Contact, about 90% of the Act! add-on market still serves the on-premise users
• LAN vs WAN: In the past, traditional workgroups operated out of one office behind a firewall on one shared LAN. Act! would be shared on one computer, and accessed from all the other workstations with the Act! Windows client. This setup was simple and fast, required little network configuration, and was ideal for on-premise deployments. In recent years, businesses have trended toward remote workers and multiple offices, which require sophisticated firewall and network configurations to support on-premise setups. Syncing databases were used in these on-premise deployments, which added more to the setup & maintenance of them. In cases of a WAN deployment, an on-premise setup is often preferred because each user has the same connection to the data, namely through the browser, and little network setup or maintenance is required.  

Depending on your business goals, budget, and preferences, you may choose either on-premise or online Act! for your CRM needs, but it's nice to know Act! users can also choose both.