You start needing to monitor your temps when you want to know more about what's going on "under the hood" as it were...
As IMOG said, the indicated temps aren't really too important as long as they are below the instant combustion range.
What they can be good for is finding hardware flaws, such as when a component is dying.
They can also be used to help diagnose imminent system failures or cooling problems.
The best way, In My Arrogant Opinion...to use temp/voltage monitoring apps is to get a "baseline" of where a system runs well, and then keep half an eye on it:
If a temp or voltage starts changing much from where it normally runs, there may be a problem.
In what passes for "normal use" in my stuff, nothing changes drastically most of the time. 99% of the time all the monitoring stuff I have set up tells me nothing other than "All is well", but its nice to have that info.