The thing to remember here "laptop" (using 2.5" drives).
A 2.5" conventional HD isn't as fast as a 3.5" conventional HD.
In this case (laptop), the advice to use SSD for tracking isn't that most folks really need a drive that sustains ~540MB/Sec for tracking... but rather it just maximizes performance in the 2.5" form-factor.
If you're working with a desktop, you can use 3.5" conventional HDs.
A single 3.5" conventional HD can sustain 100+ solid/contiguous 44.1k/48k tracks of audio.
If you're working at high sample-rates (ie: 192k with dense projects), that's when you need SSD for tracking audio.
To elaborate a bit more...
Your drive needs to be able to keep up with the load.
Having additional unused (un-needed) drive speed will not buy additional performance or allow working at lower latency.
Scale your drives based on your needs:
- Yes, you can put SSDs in RAID-0
- Yes, you can use M.2 Ultra (PCIe x4) SSDs that sustain 3400MB/Sec
If you're tracking at 44.1k... and your typical project is 24-48 tracks (not making heavy use of disk-streaming sample-libraries), you don't need to make things complicated/expensive. Dedicate a drive to "OS", another to "Audio", and a third to "Samples". Scale up from there... based on your specific needs.
ie: If you're composing huge orchestral mock-ups for video games (needing 4000 notes of disk-streaming polyphony from multi-mic position sample-libraries), then you need "the works" as far as SSDs.
Most folks don't need that level of performance.