I have several Smartsheets that have had to be broken up into two sheets because of the sheer size of the sheet and the number of complex formulas that used nested IF() and SUMIFS() functions (>1500 cells with complex formulas). These sheets would take a long time to load and even longer to save, sometimes timing out, after editing. In several cases I've been able to move the complex parts of these sheets to what I consider to be "background" processes that run entirely on Smartsheet servers rather than having to be loaded and run on my Smartsheet browser tab.
These background sheets work by having data that needs to be processed linked in from some other sheet, or via the API in some cases, processed extensively using complex formulas and then linked out to other sheets that use or display the processed data. During normal daily operations I never have to open these complex sheets. In addition to processing very complex sheets I have also generated some specialized sheets that can alphabetize or sort in numeric sequence data from some source sheet before it goes to a sheet used mainly for displaying results from multiple places. Since Smartsheet doesn't support macros or automatic sort functions there was no other way to do this. I often use Smartsheet reports for viewing data but it's not possible to use the output of a report in another sheet.
Since the extensive processing and linking is done on the Smartsheet servers it saves a lot of time loading and saving large sheets on my browser. The only downside is that when new data is introduced into my system it can take up to 30 seconds for the data to link and be processed by the servers and ultimately get to my display sheet. I'm fine with that since it all happens automatically.