Explain why. There is price, storage, and speed. Fusion drive wins two out of three.
Because its a lot more complicated than that: more + cheaper doesn't always mean better.
- the 1TB Fusion drive only has a relatively small 32GB SSD portion which may not be enough to cache all of your frequently used files. The upgrade to 2TB Fusion (with a more sensible 128GB SSD) isn't available on the 21" iMacs.
- Where both options
are available (on the 27") the 2TB fusion upgrade $200 c.f. $100 for the 256GB SSD upgrade. The difference leaves you just about enough change for an external 2TB HD for your bulky files.
- With even a 256GB SSD,
all of your OS, applications and temporary files will fit on the super-fast SSD and probably leave enough space for most of your documents etc. provided you make a modest effort to archive & keep bulky stuff (like video and photo libraries) on your external HD. Thread starter was talking about programming: unless video is involved, that doesn't take huge swathes of disc space (keep the working code on the SSD and periodically sync it to a git, or equivalent, repository on an external/NAS/Cloud drive).
- In a Fusion drive if
either the mechanical hard drive or the SSD component go wrong, you have a dead drive and your iMac is off to hospital for a week and risk losing your data. A pure SSD has no moving parts, less to go wrong and pumps out less heat and no vibration - a much better prospect for a super-slim (and cramped) machine like an iMac.
- If you do anything
remotely serious you're gonna need external drives for backup and archive anyway. - especially when you have a sealed machine where you can't pop the hard drive out if it goes off for repair. Unless you're doing something like 4K+ video editing, the
big advantage of a SSD comes from having the myriad files for OS, application, temporary, virtual memory etc. - that are being continually accessed while you work - on SSD. Loading individual data files off external drives isn't such a bottleneck (and you can always go for fast external SSDs as and when you can afford them).