Help understand server timings timeline in dax studio

[MartinBurman]

After facing some performance bottlenecks I started looking into the Server Timings page in Dax Studio to better understand what's going on. 
As you can see this expression took more than 45 seconds. We then look at the individual rows and try to se which ones take the most time and try to optimize that part. 
Question 1)
   There is a duration column, but summarizing those values only gives us the SE queries duration?
Question 2)
   If we look closer at rows 86 and forwards we see there is a huge leap from the timings indicator even though the last operation only took 1 ms. What's going on here? Is it the Formula Engine cranking for dear life without any traces? How would i go about to optimize this..?
Question 3)
   Do you recognize this charcteristic of the timeline that we have two huge operations more or less and can explain in general what could be poorly configured/usual suspects...?

[Alex87]

you have 50 queries that are 99.9% using the formula engine. You need to change the way you wrote your formula. Try different variations. Do not forget to use variables and optimize the number of queries as max as possible

[MartinBurman · Accepted solution]

We are trying! Currently we have identified odd performance behaviour with 
SWITCH
 Selectedvalue(Parameter1),
 "Option1",Measure1
 "Option2",Measure2
 "Option3",  DefaultMeasureIfNothingSelected (but as an option...)
 DefaultMeasureIfNothingSelected
 
Where the default of the switch is 2 seconds (6->4) faster than if we have selected the option that will return the same measure.