When you’re trying to design a taxonomy or classification system for something as large and complex as a country, 5 categories is better than 3, always.
Consider the differing outbreaks in Dumfries, Motherwell, Aberdeen, Coupar Angus and more recently Glasgow and surrounding regions.
Consider the different levels of infection in Glasgow, Ayrshire & Arran, Dumfries & Galloway and the Western Isles.
Here’s how the Herald outlined the 5 tiers:
While only three tiers has the advantage of being easier to understand than five, you can see the dangers in a region being squeezed into one where the restrictions don’t quite fit the evidence and, crucially, where the local population resents their lack of precision.
How the FM justified the 5 levels:
The English system starts at medium, which is quite a high level of restriction. We also think we need another one at the top because if you remember when England published theirs, the chief medical officer in England said he thought that the top level was not enough to necessarily get the virus down. We think we need one above that which is not identical to but perhaps closer to a full lockdown, if things got to be that serious.
Seven would be more precise but might cause chaos.
I haven’t seen ‘push-back; from the opposition leaders but I feel sure they’ll struggle with five.
Talking-up Scotland 'Albatraz' 
England’s Tier 3 was never considered to be ‘homogenous’ or exactly uniform everywhere, always. As a top Westminster science or public health official at a recent Westminster briefing made clear, there was a Tier 3 ‘baseline’ and then other, additional things, unspecified and uncategorised, could or would need to be implemented in Tier 3 areas. Tier 3 as a baseline was not considered sufficient.
It is at least arguable, that in order to make the case for triggering additional Tory Government funding more straightforward/compelling when negotiating with HM Treasury as the degree of restrictions needed change within Scotland, there is merit in the Scottish Government being able to align some of its its own tier interfaces with the tier interfaces in England.
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5 tiers/levels is what Ireland has had since the get go (NZ too I think), and its what we should have had.
The phased approach the Scot Gov introduced in early summer was to one-directional (I think based around the eradication strategy, but eradication only works if you have border control/England follows suit and… we don’t/they didn’t).
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