A popular question back in the late 90s, when such lenses were heavily marketed as the ultimate in consumer convenience since they cover such a huge focal length range. Sadly, the lenses tend to be fairly big and heavy, as consumer lenses go. And most importantly, the optical quality of these lenses leaves a lot to be desired. It’s very difficult to build optically sharp zoom lenses, particularly those with a really wide zoom range like these ones. The lenses are pretty slow, with small maximum apertures. They also tend to have a lot of distortion, which makes squares and rectangles in photos appear like they’re bulging in or out slightly - bad for photos of buildings.

If you only take 4"x6" snapshots then these drawbacks are probably fine, but if you ever want to make enlargements beyond that you may find that your photos look disappointingly soft - not very sharply focussed. Since they’re optically so slow you’ll probably also find that any telephoto photos you take will be badly blurred unless you use a tripod or flash. Finally, using long telephoto lenses requires a certain degree of technique and experience since the focal lengths are so long. You can’t easily handhold a slow 300mm lens, for example. Doing so, particularly without high-powered flash, is a surefire recipe for disappointingly blurry photos. And Sigma has regrettably a long history of older lenses turning out to be incompatible with later EOS cameras.

As a beginner you’re probably best off getting one or two lenses of a more modest focal length range, no matter what nonsense the salesperson in your camera shop may say about you never needing to buy another lens again. In short, consumer-level 28-200 or 28-300 lenses always suffer from tremendous optical compromises; compromises which render them of limited value, especially at the long (200-300mm) end.

There are really only two lenses with a huge focal length range that are generally accepted as possessing decent optical quality - Canon’s 35-350 3.5-5.6L and Canon’s 28-300 3.5-5.6L IS. However both are gigantic and expensive lenses not intended for beginners.