Description:
I'm not an developer, so I'm have no clue why it's working how it works. However it does seem that the file saving of large Calc files isn't that efficient. Especially for large spreadsheets (or Writer Documents)

When saving the sample file around 450 MB will be written to the disk for every regular and auto-save. As some sort of catching mechanism before saving. The exported file will be around 3,19 MB. However the caching mechanism will use all ssd drive write cycles pretty fast. 

Another oddity is that after saving the file gets loaded again. It's looking quite inefficient to me; especially for large files.

Excel is only writing the necessary stuff to the disk (as far I know of) 

Steps to Reproduce:
1. Open the attached file
2. Save a copy and monitor disk usage (process explorer)

Actual Results:  
- Around 450 MB gets written to the disk
- The saved file gets reloaded 

Expected Results:
- Less writes to the disk
- No reload (or not in this extend)


Reproducible: Always

User Profile Reset: No

Additional Info:
Version: 6.0.0.0.alpha0+
Build ID: cbf371e07fd5dea1ea08a1f299360d1273961ebd
CPU threads: 4; OS: Windows 6.19; UI render: default; 
TinderBox: Win-x86@42, Branch:master, Time: 2017-06-14_23:13:57
Locale: en-US (nl_NL); Calc: CL

and 3.0.0


User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:45.0) Gecko/20100101 Firefox/45.0