Stuffit Expander was indeed indispensable when it was included with all Mac OS installations. But at some point in the evolution of OS X, I don't remember when, the OS gained the ability to compress and uncompress zip archives. And self-decompressing dmg files became the most common disk image file format for transmitting Mac software and archiving files. Meanwhile, Disk Utility can create a variety of different image files. So Stuffit Expander gradually became less important than it once was - and the old Drop-Stuff went the way of the Dodo. Nevertheless, I still occasionally encounter archive files in a format that OS X cannot handle. On these occasions I find Expander quite indispensable. Smith Micro picked up the Stuffit franchise some years ago and has been striving to make the product relevant by expanding its capabilities. It includes some tools that a select clientele will find useful, but it no longer has broad appeal on the Mac. I give Smith Micro props, though, for making the effort to keep the product alive. Unfortunately they goofed a while back when they renamed it Stuffit Destinations. Rather than making it more appealing, they just created brand name confusion. I think they're back now with Stuffit Deluxe - though at $50 the price is daunting.
In 'the old days' the free Stuffit Expander was supposed to cultivate a market for the paid product Drop Stuff. Because hard drive space was severely constrained at the time, such a market did, indeed, exist. Surprisingly, however, you could use Drop Stuff indefinitely in demo mode - and it was fully functional. That market model was not really viable, though, so the trial period for Drop Stuff's successors is limited. Unfortunately for Smith Micro, the market is also limited.
Be that as it may, to put it politely it's short-sighted to dismiss Stuffit Expander out of hand. Just because you don't need it doesn't mean that no one will. That Smith Micro continues to develop and support Stuffit Expander - and continues to offer it for free - should be evidence of its value to anyone with a half-way open mind.