In Google Chrome on Windows, Ubuntu and I assume Mac you can go into settings and then advanced settings then scroll down to "System" and turn off "Continue running background apps when Google Chrome is closed" which might increase your PC's performance, this of course might be different for everyone as it may not help at all or help slightly for each respectfully.
If your running Windows and/or Android then you can download an application called Advanced System Care from "iobit.com", this application was my favorite PC optimizer on Windows when I ran it and is still my favorite on my Android phone, I am not sure if this application has a Mac version or not.
In Windows, you can use the "Run" command within the start menu (up to W7) or within the right click menu (by clicking the windows button in W8+) and typing "msconfig" and hitting enter, once the window pops up there will be a few tabs at the top, click the services tab and then near the bottom tick the hide windows services, once that's done then you can go through the listed services and disable the ones you don't need or want, once that's done restart your PC , this may or may not help with the speed of your PC.
Defrag has the potential of greatly improving you PC's speed but only if you've never ran it before, defragging is recommended to be done at least once a month to two months, but if you've owned your PC for a year or more then doing this may prove to be a good thing, as a side note, do not defrag if your PC has a Solid State hard drive (aka SSD), reason being is that running defrag on an SSD can reduce the life span of said SSD, do not defrag any Android device either as they use SSD.
If your running any of the Ubuntu OS and basically live on the net (meaning you backup all of your documents/etc to Google Drive or One Drive/etc) then you can keep a copy of your Ubuntu installation on a Flash Drive and just reinstall if your Ubuntu system becomes slow or corrupted, I know there will be someone that's going to make some kind of comment that's going to say something close to "Ubuntu doesn't slow down" or something, to you I say that's not everyone's experience I can assure you....
If your running Ubuntu and want to install applications easily then you can search for your application in google and at the end of the application name type ".deb" or "terminal install", example "Skype .deb" or "Skype terminal install" this way if you can't find the application within your application store then you can easily install it anyways.
Do not add a bunch of different file managers to your Ubuntu installation and if you do add more and decide you like one then remove the others from your system because by leaving them installed you may slow or even damage your system.
If your Ubuntu installation has become damaged then it might a good learning moment, instead of just reinstalling Ubuntu use your phone or other internet enabled device to search out information on how to repair it your self so you can increase your knowledge of the terminal.
If your looking to share files between multiple PCs (Windows to Windows, Windows to Mac, Windows to Ubuntu or any other combination) then check out "NitroShare" for easy file transferring.