Responsive Web Design!
Long gone are the days when people's only internet usage was made up from when they used
to come home from work,
sit down besides their desktop computer and browse the internet for a couple hours,
before turning it off again for the same time the next day.
People want the internet 24/7 these days, whether they're at home or on the move, especially the younger generation. If you want to attract as many visitors as possible to your site, then you need to be able to cater for everyone's preferences. Having a website that isn't responsive to all devices is almost suicidal in a business sense.
More often than not, visitors will leave your site in a heartbeat rather than persevere with a website that doesn't function correctly. This can not only affect your bottom line, but it can also have a negative affect on your websites SEO too. If a visitor to your site immediately clicks off it, it increases your websites bounce rate, which in SEO terms is bad news for your browser rankings.