Yes. I don't fill my hard drive more than 2/3 full.

It is not the same thing that happens with mobile phones, the occurrence of slowing down the pc, is the product of several factors this is common needs resent updates, this is the time that one sees that one sees that it is getting slow is that you need to defragment it which returns to have its performance well, some errors fix damaged files and starts things to not work properly and is frisa and takes a long time.

It is necessary to have antivirus.

malware or malicious program and it is one of the problems also much more common that makes the pc present problems of damage of files, replicas and intalandose things by installing a program that is infested.

Of course, imagine a car park full of vehicles and one with very few, when you get to the one that is almost empty you choose where to park and you spend less time as opposed to one that is full, you spend more time looking at where to park.

Now change the parking spaces to disk sectors and the vehicle you are driving to the information you are going to save.

What you can do is defragment the disk to sort sectors so that the read/write head doesn't spend so much time looking for a free space.

I have seen computers running normally with the disk 90% full, what should be monitored from time to time are the open processes, the existence of viruses, the cache memory of the different programs that make use of it, mainly browsers, everything that is running at any given time, spending ram memory and processor resources is what can really slow down your computer, although it is good to defragment the disk from time to time, even if the disk is not very full