I have had cases where the user has gone a full year with no need to optimize anything and had other cases where the user had to literally format the PC after a month. The 1 year guy used the computer for word processing and internet only.
The 1 month used it to download a lot of stuff, music, videos, games, deleted some, moved some, etc..
In all of this time, both did not do any optimizations.
Performance wise, Ubuntu (or any other distro for that matter) is not influence in performance by the amount of garbage left behind in the system that fills the HDD.
That is a Windows problem not a Linux one where, if you get around 25% to 35% of the space left, the system starts slowing down (Shown more in Windows XP than in Vista or 7/8).
Anyway, like I said before, having a 99.99% hard drive full of stuff will not slow you down.
In case I never do a cleanup, will I have a system like new without my hard drive being full of temporary files, packages, etc.?
Will the performance degrade overtime if a cleanup is not done. In windows you need to do a cleanup mostly every week if not every day (I use as an example the fact that I worked in over 30 cyber cafes which are in total more than 500+ PCs.
The work the got from users made having to cleanup everyday a typical job.).In Ubuntu, this cleanup is actually not needed so often, but if you actually need to do it you have several command line tools like that also do this.The cleanup for Ubuntu can be done every 6 to 12 months.Yes that is right, every so many months you can do it or in my case every 2 or 3 years.This really depends on the amount of work you put the PC through.When I say work I mean, downloading files, moving files, creating files, deleting or copying files. Most Windows users know that the performance of any Windows degrades really fast if no optimizations are done.