Some people buy an SLR because they are told SLR takes good pictures. Others buy the point-and-shoot digicam because they find that the features are all available as in an SLR. So what really is the big deal about an SLR over a digicam apart from interchangeable lens? There is nothing special about an SLR that could not be produced in a digicam if the manufacturer so desires. They would probably do so if it makes commercial sense. An SLR simply encompasses a certain level of features and performance, rather than an exclusive technology.
If you are undecided between an SLR and a digicam, here are some points to consider whether you really need an SLR:
1. Interchangeable lens
Obviously, this gives the SLR flexibility in the use of superior optics to achieve a desired effect. If the shot is achievable in a normal digicam, then the SLR will not contribute very much to producing a better shot for you, generally speaking.
2. Bigger sensor
The much-larger sensor in an SLR has better light capturing capability, thus expanding the range of ISO you can use. In an experienced user, it enables you to shoot with a shallower depth of field for creative effects. This latter advantage is seldom exploited by a novice photographer.
3. Faster shooting
Although digicams have improved tremendously in this area nowadays, a typical SLR still outperforms the digicam in how fast you can shoot. There are 3 key areas: the shutter lag, the time between shots, and the focusing time. When you are shooting an event, every second counts. That is when you need a fast trigger.
Bearing in mind the above three reasons, it is easy to see why a normal point-and-shoot digicam is all a person needs while on vacation. The quality or performance edge of an SLR sometimes does not justify the extra baggage you need to lug around. On vacation, you are seldom looking for outstanding creative shots (which is hard work), you are mostly shooting in broad daylight (even in non-ideal midday sun), and you typically shoot at your own pace (don't need a fast trigger). Having said that, I still carry my SLR on vacation, but shoot with a digicam unless I really need to pull out the SLR.