While pedalling can help out with legato lines in a pinch, that is not the sole purpose of the pedal. One of the most useful effects of the pedal has to do with what actually happens when you play the pedal. When you play a single note, the damper for only that note is raised off the string, allowing the string to vibrate. If you play the same note, this time with the pedal depressed, ALL the dampers are raised off the strings, so then not only will the string the hammer strikes vibrate, but there will also be sympathetic vibrations on the other strings that are related through the "overtone series" to the string the hammer strikes (meaning certain notes, based on their frequency, will vibrate more than others -- making a louder sound in the process). This makes the sound you create sound much fuller than had you played it without first depressing the damper pedal. In the end, the sound you get with the pedal is not necessarily louder, but there are harmonics you won't hear if you don't use the pedal.
Topic: When should I use the right pedal?