You're right, these are very similar categories! As I think you implied from your question, there isn't much OOTB impact by having separate financial categories because they're both referenced in these two metrics, and are only calculated separately when referring to themselves:

(source documentation)

I think mileage can vary depending on the customer, but here's my personal take on why it may be nice to break these two categories out:

Other Operating Expenses Financial Category:

Because operating expenses can differ depending on what a company does, the various other OOTB Financial Categories provided in Fusion Data Intelligence may not capture all of the Operating Expenses that apply to a particular company. That's where customers can group all of those remaining natural accounts to the "Other Operating Expenses" financial category.

Miscellaneous Operating Expenses Financial Category:

Now let's say that a company has a natural account called something along the lines of "Miscellaneous Operating Expenses" to pick up any one-off operating expenses that they don't have an existing natural account for because they happen so infrequently.

But perhaps as an analyst, you want to be able to quickly analyze if expenses in this category are growing over time or abnormally (Example analyses: Are expenses being booked here miscategorized? or: Should the company consider creating a new natural account if balances in this account are from similar suppliers?)

If the company assigns this natural account to the "Miscellaneous Operating Expenses" financial category, the analyst will be able to easily keep an eye on this through a simple drag-and-drop of the metric.