That rating you mention is just an arbitrary number which the speaker manufacturer believes will satisfy most listening habits. Generally, most people tend to prefer to be on (or over) the high side and use their ears and common sense to tell them when the speaker/amp combo is reaching it's limits and turn it down.
Too low power and you might not get the full range your speaker is capable of producing. While most "average" listening is done with between .5 - 1 watts, turning it up, even slightly increases the demands in the amp exponentially.
To put it simply, a barely audible increase of 3 decibels requires twice the power. That aforementioned number is now 1 -2 watts. To double the apparent loudness of what you're listening to (which is easily accomplished with musical peaks) requires ten times the power. Now we're drawing 5 - 10 watts. When you consider that many peaks are more than double the average listening level.it's easy to see where problems can arise.
When you consistently put more demands on an amp than it can deliver, it distorts in a manner called "clipping", which is not a good thing for the amp, the speakers, or even your ears.
But, if you're happy with listening at consistently low, even background, levels, you should get by with your current situation.
IF you want this worded in a more professional manner, click on
this link.
If you want to get a more "real world" idea of what these decibel thingies are and how they relate to what you are actually hearing, click
this link
With these two links, you should be able to "do the math" for yourself and determine if you feel what you have is sufficient. Hint: you might want to check the sensitivity rating on your speaker. That's fairly important to any answer you might get.
