I didn't set out to buy a combination machine. In fact, I was poised to buy a free-standing tablesaw, jointer and planer to outfit my new shop seven years ago when a friend told me he was selling his Robland X31. My shop space certainly was tight -- about 430 square feet in an L-shaped configuration. But I'd always thought of combination machines as lightweight and gimmicky. My friend talked me into giving his Robland a look, assuring me it was no lightweight.
After trying out all five functions (sliding tablesaw, jointer, planer, shaper, and mortiser), I was impressed. Anchored by 1,100 lb. of cast iron and steel, and powered by three separate 3-hp motors, the machine performed each task smoothly and efficiently.
Intrigued, I went home and considered the Robland more carefully for my shop. Now the space seemed even smaller, even more suited to a combination machine -- which is to say, I was leaning toward making the purchase. But even at a used machine price, the Robland would be more expensive than separate used machines of similar size and quality. More importantly, I'd have to pay for it in one lump sum. And while I'd used a shaper and mortiser extensively in my previous employment, I didn't plan on getting these two machines at the outset for my home shop. Still, having more machines could only be a good thing, right? After tweaking the terms of the purchase, the deal was done.
After seven years of trouble-free use, it turns out that a combination machine was very suited to both my shop space and the kind of projects I do. After buying several smaller tools (chop saw, bandsaw, router table, drill press, belt sander), and finding the best arrangement for them around the perimeter of my shop, the core space had shrunk considerably. In retrospect, having a separate tablesaw, jointer, and planer would have been far more problematic than I had anticipated.
You'll notice that my list of ancillary tools provides some functional overlap with the typical combination machine: With a sliding table saw I could make crosscuts without needing a chop saw, and the router-collet adapter for the shaper makes a router table expendable. But this gets to the practical logistics of working with a combo machine in everyday use.