Seq resizing

[Arrrrrrrrr]

I did some tests, and looks like a seq is resized before actually needing it:
    
    
    proc main(useAdd: static[bool]) =
      const TOTAL = 10_000_000
      var s: seq[int] = when useAdd: newSeqOfCap[int](TOTAL)
                        else: newSeq[int](TOTAL)
      
      for i in 0 .. <TOTAL:
        when useAdd: add s, i
        else: s[i] = i
      
      echo "----"
      echo "LEN: ", len(s)
      echo("SIZ: ", (len(s) * 4) / 1024)
      echo "RAM: ", getOccupiedMem() / 1024
      echo "----"
    
    main(false)
    GC_fullCollect()
    main(true)
    

this prints: 
    
    
    ----
    LEN: 10000000
    SIZ: 39062.5
    RAM: 39120.0
    ----
    ----
    LEN: 10000000
    SIZ: 39062.5
    RAM: 88948.0
    ----
    

I would expect the resize to occurs when seq actually needs it, and not before. 
Maybe i want to make sure a seq doesn't take more space than needed. But if i'm 
right, i might need to give it +1 size to avoid the resize. Am i wrong here?