Is it safe to delete from C:\Windows\Installer?

"No, it's not. Windows Installer uses that to cache installation files for anything installed on the machine using Windows Installer. At a minimum, you could lose the ability to add or remove programs, at the worst, you may lose the ability to run some programs.

Since Windows Update can also deploy Windows Installer patches, you could also prevent your machine from receiving Windows and Office updates."

"As others have said, there are definite contraindications for removing files from that directory structure. I would also recommend against it.

However, if you are determined to proceed anyways, you can more properly do so using the Windows Installer CleanUp Utility. This will clean things up better than simply deleting files. This tool is, however, generally used for removing installation files that have become corrupt thus preventing you from uninstalling something the normal way.

The Windows Installer CleanUp Utility actually uses the MSIZAP.EXE command-line utility to perform the work."

"If you delete this folder, you will experience issues later when you attempt to repair, uninstall, upgrade, reinstall, etc.

The way MSI installers work is they run themselves whenever a patch must be rolledback, something uninstalled, etc.

Future Windows Updates may need the contents of this folder.

MSI installers are the devil :() Don't toy with them."

"As other answers state, it is not safe to delete the Windows Installer folder completely.
But here are some popular practical solutions to safely move or shrink it:

How can I free up drive space from the Windows installer folder without killing Windows?

Personally I used PatchCleaner that helped me to knowingly reduce Windows\Installer size from 23 to 3 Gb by moving orphaned packages (mostly M$ Office 2016 updates)."

"When disk space is running out on a system disk, may it be on a server or a client, there are certain things to clean out. One of them being the %SYSTEMDRIVE%\Windows\Installer folder. You cannot under any circumstances delete files from this folder manually as this not only may but most likely will break software that is installed using MSI files, or Windows Installer files.
The %SYSTEMDRIVE%\Windows\Installer folder is a cache for installation files and patches (MSP files) and removing those will cause you to not being able to repair or uninstall applications, and in some cases not removing patches or applying new patches to software. In the event when you actually did delete this cache you can rebuild the files you need manually by extracting the files from original installation media, from patch packages etc but this is a time consuming and not that easy task to accomplish.

Andreas Stenhall, MVP Windows Expert ITPRO
Ref.: http://www.theexperienceblog.com/2009/05/16/how-to-clean-out-windowsinstaller-folder-correctly/
You may try to make some SAFE cleaup with this MS Fix It utility:
Diagnose and fix program installing and uninstalling problems automatically"