Sheet Efficiency & Size

I work in a large international bank and am responsible for producing the daily profit & loss report for the global operation - the spreadsheet that does this is currently a bit of a dinosaur and so I have made a new slimline one with more functions that I am rather proud of - for example I have managed to avoid VLookups almost comletely, opting instead for Sumifs and Array (CSE) formulae - basically I am after any general tips on reducing file size and or increasing calculation efficiency - one interesting idea I had was is it possible to reduce the size of worksheets as most of mine do not have more than 4000 lines per sheet and less than columns AZ:AX - would removing all the excess area help?

Any help much appreciated - This is my first post to the board.

Rgds
Phill