Correct alignment of fans in the machine is also one of the reason , I had an experience regarding fans kept the laptop on the bed for hours and used to browse .
The dust particles or fibrous material were absorbed by the machine , after a long time when i sent the laptop to the apple service centre they opened the machine and showed the fibrous material , and of course they cleaned it .
Some advices were given keep the computer on hard surface ( keep it on the table ) if it is perforated then performance will be excellent .
Also when data is transferred spotlight indexing can occur , and the CPU percentage will come down after days , if any process is exceeding 70 % then something is problematic .
Spotlight indexing is a normal process , when you shut down the system and open an application example mail you will see a bar is loading ( as system and the processes take time to boot ) .
Note : Avoid opening multiple applications at the same time , use a single application when your task is completed quit the application then use the other application ( I have seen some users , they have opened many applications say , calendars , notes ...etc from morning to evening and are browsing and at the end of the day forget to quit one or two applications and shut down the Mac , the applications will be running in the background that has not be done .