These days, many people are always online in some way, via their smart phones, tablets, or via their laptops. It doesn't matter if you're not at home, if you want to you can be reachable at any time. For some professions, this is a necessity, but for a lot of others, it isn't. While we think that the Internet is great, we also think that people should log off now and again.
In the past, I used to work in finance and I spent hours yapping away on my cell phone. I spoke to clients and my employees, often for hours a day. I had to be reachable almost 24/7. I worked on weekends. Since 2006, I've actively eschewed cell phones. Over the last few years, I've stopped using instant messaging. I still use Skype, but I no longer want to spend hours on an IM client.
Disabling email notifiers is also a good idea. If you use Inbox Zero, there's no need to know when you receive new mail. Checking your email a couple of times a day is enough. Cell phones and emails can be seen as an electronic leash, especially if most of your electronic correspondence pertains to work-related issues. Checking my email can entail work, which is why you shouldn't leave a tab open all of the time.
This is one of the reasons why I completely log off after my work day. Spending hours online after coming home from work doesn't really force you to go out into the world and be active. Time online means that you're sitting on your chair typing away. While there are benefits from social networking, it's usually best not to over do it and spend time outside.
Taking a book to a nearby café, taking your dog for a walk, and spending time getting into shape are worthwhile endeavors and pleasures that are easy to forget if you spend your free time glued to your screen. If you live with your partner, it's nice to take time after work to eat a meal together, switching cell phones and computers off for a while. Sitting for hours at a time isn't very good for your body. In fact, it's really bad.
One of the tricks I use is that for most of my work-related surfing, I use Firefox. When I log off, I close this browser and use Chrome if I need to check up on something.