Do I Need a Hub to Automate My Home?
A lot of people in the home automation field are suggesting that the home automation hub (e.g., SmartThings, Wink, Vera, etc.) is no longer necessary. With the plethora of WiFi devices available today that connect directly to an app on your phone, hubs are just an extra layer of complexity. Well for some use cases, that is probably true. For example, you would like to be able to turn on a lamp (or another device) while you are away from home. You could plug the lamp into a Wemo outlet and use the Wemo app to control the device from your phone. At this stage though, you haven't implemented home automation, you've implemented remote control. The Wemo app (and most apps for other WiFi-enabled devices) support simple automation such as adding timers or scheduling. However, you will typically be limited to using products from a single manufacturer. If you have devices from different manufacturers, you will most likely have to open multiple applications to control the devices. Most hubs (especially SmartThings with its active user community) support devices from multiple manufacturers and using different protocols including ZigBee, Z-Wave, and WiFi. If all of your devices are connected to your hub (even if they use different protocols) you will typically be able to control them from a single app, or even all at once using a store routine on your hub.
Many might consider the Amazon Echo or Google Home voice assistants hubs. While they do provide many of the features and capabilities of hubs, they aren't really a substitute. However, I would consider it essential that whatever hub I chose support at least one and preferably both of these devices.
A home automation hub will typically support greater "automation" than standalone apps. For example, the SmartThings hub allows you to set up routines. Routines allow you to control multiple devices, from different manufacturers, setting different properties based upon what is supported by a specific device. Among the most powerful automation techniques that hubs make fairly easy to implement is control a device, or initiate a routine controlling multiple devices, via a trigger. The trigger may be a switch, or a sensor detecting some change in state such as movement, light, or presence of water. That last one is one of the most useful triggers that I will be implementing soon in my home to provide protection against flooding.
Scheduling through a hub can also act as a trigger to initiate any of the events outlined in the previous paragraph. Scheduling can be implemented in a way to simplify your daily routine by automatically turning lights or other devices on and off at predetermined times customized around how you live in your home. Schedules can also include some limited randomization to impersonate a "lived in" home when you are away.
Although there are improvements coming in power management for WiFi devices, most still are considerably more energy-hungry than ZigBee and Z-Wave devices. This makes them less suitable for battery powered devices such as remotes, buttons, connected locks, and sensors (including motion, light, temperature, and leak.) Batteries in ZigBee and Z-Wave devices typically last a year or more. This is especially important for devices that may be installed "out of the way" or "difficult to access" places.
Hubs themselves tend to be fairly inexpensive. Some of the proprietary protocols can add to the cost of your other devices. But, for the reasons outlined above, if you are planning to install more than one or two smart devices in your home, I recommend building your system around a hub that provides the features most important to you.