Maintenance
Mostly your Mac will do essential maintenance such as defragmenting by itself. There are also daily, weekly and monthly maintenance scripts to run which is why it is true that the computer likes to be left on continously so that these can be performed.
I have found that a little preventative maintenance goes a long way and it is simple to do. Apart from the afore mentioned scripts there are caches for a heap of different things. Caches are areas where data is stored for quick retrieval. Internet caches, print caches, system caches and more… and the nature of temporary stashes like that is that they are more likely to become corrupt because there is data constantly being added and removed from them. So its a good idea to regularly clear them and what better way than by one of several small applications on the market that do all the little things that make your computer happy, including clearing caches.
I use Cocktail a freebie from Maintain. Download it, install it, configure it and run it weekly and all should be well! Barring major problems that is.
You can also buy it for the reasonable price of US$15 which means you can schedule it to do the weekly run.
Once it is installed open Cocktail, enter your account password and it will ask you to Register. Click Cancel and this window will appear, but without my Single User License info:





If you buy Cocktail then you enter your serial number under the Cocktail menu/Registration and when Pilot is open click the Scheduler tab:







