Storage Sense and Compressing drive C?

Now that Reserve Storage has reduced storage available to about 2 GB I am begining to experience some issues, even having done my usual cleaning routines. There might still be something more to gain from cleaning up further in Storage Sense. Download Files appears to have over 8 GB available but I have not got it to free up anything despite trying many times. Why is this and is there a way to get it to work? Secondly, Compressing the drive should shrink it by over 10 GB. This is something I have not done before ---- what are the pros and cons?

Thanks for the many useful links. Having had a 'small storage device' for a few years I have checked / used many things to reduce demands on the C drive, including removing Windows.old (I thought it was uninstalled automatically after 10 days anyway?); and Hibernation has never been activated (as is common with Tablet PCs). I use Disk Cleaner almost every day, now most often via Cleanmgr+ which is meant to replace it. Incidentally, the most effective cleaning app among several I use such as BleachBit and CleanSpace7 in addition to CCleaner (enhanced), is part of SystemUtilities ---not so well known I think.

Yesterday I decided to try the Compress option in Storage Sense, as it can be reversed if necessary. The 'bad news' is that it only saved about 2 GB, not the 10 GB suggested in Storage Sense which is still showing 10 GB to be available. The 'good news is that I have not (yet) found any negative consequences of compression, if it has slowed the system down it is not noticeable to me ---- I would not know drive C is compressed were it not for the changes it makes to folder icons. Which means that while 2 GB gain is not what I expected it is still worthwhile.

Also, Storage Sense still reports 8 GB to be available in Downloaded files with no sign that it is cleaning them when set to do so. So I still have more to find out about the failure of Storage Sense to do what it is supposed to do. It looks like I may have some time before the attempt to install the May update.

Since I started this thread I have learned that Reserve Storage was not installed on my machine. Which means that the disapearance of 7 GB from my C drive is not explained and is a more serious loss than I first thought. I will not be able to install the latest feature update (July?) unless the use of an external flash drive still works, as it has done in the recent past. I would have assumed that it will work, were it not for the fact that it has not been mentioned in any of the confused / incorrect articles about Reserve and minimum storage requirements, which have undermined my confidence.

Hello and thanks for the suggestions. My ver is 1809 so I had not expected to find Reserve, but suddenly 7 GB (a large %) of my free Storage vanished, leaving me with only 2 GB (and devastating my Desktop.) When I found in Settings my Storage on C was listed as "Storage and Reserved", plus the coincidence of it being 7 GB that is 'missing' I wondered at first if the Reserve had been installed in preparation for the update. This seemed more likely when I got messages from MS saying that my PC was "being prepared for the update". However, I have found now that I do not have the Reserve, so the strange shrinkage by 7 GB and the even smaller free space remaining is a significant issue. I only had 2 GB left!

After starting to use Tree Size as you advised and a number of cleaning tools, I have so far been able to get back to 5 GB, still too small. I am now being told (in Settings) that the update is ready for me to install when I wish. But what might be the consequence of trying to do so, especially if it wants to create 7 GB Reserve out of the mere 5 GB I have? So before trying, I want to find / create more free GB.

I don't have Windows.old or hibernation enabled, or any (unnecessary) big files. I download all I can to my integral SD card, to which I transfer videos, images, documents and all apps / programs which will move (some wont). Tree Size still says I have 7.20 GB Programs and 6.3 GB Windows Apps on C, so perhaps there is more I can do here? I am told I can transfer the Libraries themselves, which I will do. There are two issues in particular I am confused about (1) Storage Sense does not seem to work correctly, despite running it several times it still shows about 8 GB to be available in Downloads, and 10 GB from Compression after my OS has already been compressed. If this is genuine and can be released it would make a big difference (2) Tree Size shows One Drive as having 16.6 GB in use when in my innocence I was expecting it to be almost empty, a point of One Drive being to keep things in the Cloud not consuming space on C. I am in another discussion in this Forum, trying to understand this and the difference between Size and Allocated, Size on Disk.

PS I meant to add that I dont use System Restore now, and I have noted to look for wer & dmp files to clean. Plus in Space Sniffer (similar to Tree Size) all the files in One Drive are shown as .htw files which unlike files in Tree Size I have not been able to open / play. Does this mean that they are not really taking (much) space on C and are like the placeholders we used to have?

I moved the h2w files to the D drive, an SD card. Free storage on C increased from 5GB to just over 19 GB, a very good result. I am ready to try installing the May / July update tomorrow. Then I will try to find fixes for other issues.