I did a google search for keyword “Office 365 multi geo performance” and found below results.

What does it mean ?
If you are enabling Multi-Geo in Microsoft 365 to fulfill your Data residency/regulation/compliance and Data in Rest requirement, would it not help to improve your end user experience ?. I believe, It’s a debatable question even Microsoft does not agree upon it and the claim that they have word-class Microsoft global network optical fiber mesh across the global with super low latency.
I am not a Network expert, but the definition of latency says that latency is directly proportional to miles, meaning more miles more latency. Also, A single mile of cable produces 0.5 percent of the delay introduced by a 200-mile stretch of cable as per the research.
Let’s consider that company “ABC” has office in 3 city’s and M365 tenant is hosted in Frankfurt (Germany). Take the used case for user email connectivity for three locations.
- Germany (Frankfurt) (Headquarter) – Employee count (2000)
- India (Pune) (Ops) – Employee count (12000)
- NA(Philadelphia) (Sales and marketing) – Employee count (500)

Users based in NA(Philadelphia) are sales and marketing people those travel lots and mostly do connect from different countries and reach to Microsoft nearest front door locations, So far so good.
Users based in Germany (Frankfurt) are connecting the Microsoft data center located in Frankfurt and would have better performance and experience.
India Users(Pune):-
Users located in Pune (~12K headcount) first connecting to Microsoft Pune front door and then routing to Microsoft Frankfurt data-center where tenant is hosted.
SO, Total latency (Outlook Connectivity) = Employee location to Microsoft front door(ms) + front door to Microsoft back-end (ms)

If you have opted the Multi Geo for India users and moved all their mailbox data to Microsoft India location (Pune).
Total latency = Employee location to Microsoft front door(in ms) in Pune

So while users connecting with Pune front door, they are reaching in <10 MS (of course depend upon the ISP and egress performance) and they should have better experience.
So, Summery of this post is – I am not saying that you simply take the call to enable Multi Geo and pay 2$/User cost and you will see exponential improvement in performance, but you can take this consideration into account while you are working on to overcome Data Residency requirements and engage your Microsoft partner and consulting services (MCS) to plan it.