Improving efficiency of a Google sheets script - google-apps-script

Question

I'm fairly new to Google script and have been basically cobbling together code by finding it in Stack Overflow answers or the Google documentation. I have a working script, but it's very slow, so when I try to run it on a large file, it times out.
I know there must be inefficiencies in my code given how I went about writing it, but since I'm not super familiar with the language and learning as I go, I need help understanding how to find them (or help finding them, or both).
The code basically goes through a file that is a series of datasheets, each with a block of data that I need to copy into a "master sheet". Basically it's copy and paste, but from sometimes over a hundred sheets (which is why I'm not just doing this by hand).
Code in question (excessively commented, I know, but I'm not the only one using it):
function CleanAllTheThings(){
//Define all the variables first thing
var ss = SpreadsheetApp.getActive();
var allsheets = ss.getSheets();
//Get rid of blank rows and columns so Google doesn't get upset
for (var s in allsheets){
var sheet=allsheets[s]
var maxColumns = sheet.getMaxColumns()
var lastColumn = sheet.getLastColumn()
if (maxColumns-lastColumn != 0){
sheet.deleteColumns(lastColumn+1, maxColumns-lastColumn)
}
var maxRows = sheet.getMaxRows()
var lastRow = sheet.getLastRow()
if (maxRows-lastRow != 0){
sheet.deleteRows(lastRow+1, maxRows-lastRow)
}
}
//Continue defining variables
var create = ss.insertSheet("Merged",0);
var destsheet = ss.getSheetByName("Merged");//Name of sheet you’re putting everything into. If you don’t like the name, change it, but make sure you change it in the for loop too, or it’ll give you an error
//var StartRow = 4;//Row to start with, must be the same for every sheet; change it if the data start in a different row
//var StartCol = 3;//Column where the actual data start, ditto above
//var EndCol = 11;//End Column of all data, ditto above, but shouldn't ever change unless there are more columns--then just change this number accordingly
var prOne = ss.getSheetByName("Profile 1");
var rows_deleted = 0;
//Create a Merged sheet
for (var s in allsheets){
var sheet=allsheets[s]
if (sheet.getName() == "Merged"){//If the sheet is called “Merged”, don’t do anything to it!
}
else{//If the sheet is not called “Merged”, do stuff
var EndRow = sheet.getLastRow()
var copyRng = sheet.getRange(4,3,EndRow,11)//If the data start in a different place than row 4 column 3 and end in a different column than column 11, you need to change these numbers. Leave EndRow alone because it changes
var nextRow = 1 + destsheet.getLastRow()
destsheet.insertRowsAfter(destsheet.getMaxRows(), EndRow)//insert rows so Google doesn’t have fits. You end up with extras but you can either take them out with the add-on or just leave them be. I don’t think they’ll fill with ###### when you bring them back to Excel, if that’s what you decide to do
copyRng.copyTo(destsheet.getRange(nextRow,2))//Row and Column of where to paste the information; you’re pasting into column 2 because you’re about to fill column one with the sheet name the data came from
var LastRow = destsheet.getLastRow()//New last Row after pasting the data
var Sample = sheet.getRange(1,1)
sheet.getRange(4,2).copyTo(destsheet.getRange(nextRow,1,LastRow-nextRow+1,1))//Paste the name of the sheet in column 1 for every row copied
}
}
//Add a Header
prOne.getRange(3,3,3,11).copyTo(destsheet.getRange(1,2,1,10))
prOne.getRange(4,1).copyTo(destsheet.getRange(1,1,1,1))
//Get rid of the Solvent Peak rows
var range = destsheet.getDataRange();
var values = range.getValues();
for (var i = 0; i < values.length; i++){
for (var j = 0; j < values[i].length; j++){
var value = values[i][j];//row numbers are 1-based, not zero-based like this for-loop, so we add one AND every time we delete a row, all of the rows move down one, so we will subtract this count
var row = i + 1 - rows_deleted;//if the type is a number, we don't need to look
if (typeof value === 'string'){
var result = value.search("SOLVENT PEAK");//the .search() method returns the index of the substring, or -1 if it is not found we only care if it is found, so test for not -1
if (result !== -1){
destsheet.deleteRow(row)
rows_deleted++
}
}
}
}
//Delete blank rows and columns in Merged
var maxColumns = destsheet.getMaxColumns()
var lastColumn = destsheet.getLastColumn()
if (maxColumns-lastColumn != 0){
destsheet.deleteColumns(lastColumn+1, maxColumns-lastColumn)
}
var maxRows = destsheet.getMaxRows()
var lastRow = destsheet.getLastRow()
if (maxRows-lastRow != 0){
destsheet.deleteRows(lastRow+1, maxRows-lastRow)
}
}
For one thing, I know adding blank rows that I later delete is just a waste of time, but I'm not sure if it's such a big waste of time that fixing that alone would help this.
Thanks in advance for any help!