"It's convenient". Sometimes. It can be very inconvenient if you can't find what you need in a reasonable amount of time.
"It's free". Up to a point. Most of us pay low monthly fees for internet access, and some of the resources that are available online are free. Ever done a search and found the perfect "article," only to discover that to get the whole thing you have to pay for it? Argh!
"It's current". Sorta. Some of what is on the web is very current. But some of the web pages out there were created five years ago and have never been updated since. Don't assume that information is current just because it's on the Web.
"It's interesting". Something about the Web is just more fascinating for many of us than books. For one thing, books just sit there. No flashing, spinning images to hold our attention. No quicktime movies or shockwave video. And books are very linear, while the web allows us to sample information from various sources in quick succession and explore more freely.
While we are surfing from one web site to the next, we may find we have substituted entertainment value for substance. A lot of what is on the Web may be free and flashy, but it's also ... well ... shallow and, in some cases, downright deceptive.
The characteristics that make the Web fun also make it problematic for serious research.