On subjective sensations (tests not conducted) at the speed of the computer affects the number of objects in the profile folder, including the documents and on the desktop.
It is the quantity, not size: if it weren't for the trash on the desktop, it is better to pack the garbage in the archives and the labels are stuffed in folders. So everything will work much faster.
Fault is most likely FS. Anyone who has worked with a large number of objects, probably noticed that the folder can be hundreds of thousands of objects, and they do not manifest themselves until you open the folder - then start the infernal brakes.
Ie blame the fact that the profile is always open (the system and by many applications), and very often there are appeals, so posting there once is not recommended.
And the reason of brakes, including folders on the desktop, shortcuts, and Start - not the amount of memory and disk access.
When you upgrade your desktop system has to rediscover each label, i.e., download from disk and parse each file label to find and load to it icons, open the folder referenced by the shortcut (and it generates another flurry of calls to FS), check out the links to the executables and who knows what else. And so for each label.
If on the desktop are folders, the situation is even worse: for each folder, the system needs to draw the icon content, to do this, she opens the folder and checks each file in it, and if it finds media files - parses them, generates the icon, then selects a few icons, and one of them generates the folder icon. At the same subfolders inside it looks. So simple rassasyvanie trash folder saves - even if the case be in a folder where lay the debris, a subfolder with the garbage no one will not scan, and therefore the debris will remain intact, and these hundreds of thousands of files will not slow down the system.
And all this applies not only to the desktop - and in General to any visible folders and files in Explorer, and those where we address different program (any documents, local, etc. through folders, hood popped every program).
Therefore, it is popular alternative FM, which do not suffer from such garbage, not generates tons of queries to disk for decorations.
Unnoticed all this can be only if you have SSD. But quietly - not so good: let all-it eats a small portion of i/o SSD, but nevertheless eats and useless - it is better to leave these resources with other applications, especially the performance of the SSD on such tiny transactions very end, about 50-70MB/s, and it is easy to eat.
The situation is complicated NTFS each time you access a file it overwrites its attributes (last access time), and then throws them to disk (synchronous writes, to bypass the buffers), it eats up to half the speed of the disk. This feature can be turned off, and to ease the life of the drive. Yes, and SSD is not what the constant overwriting MFT.
Well, as a bonus, on top of all of this circus sits the indexing service, and continuously monitors the system disk, generating the extra queries. It is also better to kill, and for seeking to use a faster tool like Everything or SwiftSearch.