Portlet Preferences Usage - Best Practices

PortletPreferences should be used very carefully and in situations only when there is a valid use case for it.
So ideally, one should have good knowledge of portlet preference and most imortantly, where to apply it.

The PortletPreferences object provides the ability to store information persistently about how a client wants to use a particular portlet. 

For example, with the stock portlet, a user can provide stock code information to the portlet, and the portlet will store that information persistently using the PortletPreferences object. The next time the user visits the view mode of the portlet, the stock details for that user's choice will be displayed. 
Persistently storing this information, is all done behind the scenes for you by the portal framework.

So when you use portlet preference, did you ever think about where does portlet preference gets stored? In hard drive, some KB's data in DB or as CLOB or something that is not efficient. 
So how to store portlet preference is completely upto portal vendors and hence we as a developer or DB administrator don't have much control over the data which is stored in portlet preference.

Let's talk about application efficiency, where in if you want to store just a Boolean flag and if you choose to store it in portlet preference, you don't know how it will be stored and what size it would use for storage compared to if we chose to use our own DB to store the flag which would just take few tiny bit of space.

Furthermore, mining information from data stored in portlet prefernce is almost very difficult.

So, If you don't know how the portal stores your PortletPreferences data, and you don't know how the portal ties a particular preference to a particular user, you're going to have a pretty hard time mining your own data.

The best use of portlet preference could fall in below situations where a user wants 

1) To have red background.
2) configurable pagination numbers
3) configurable TimeZone
4) configurable portotol ( http or https etc )
5) Configurable fonts etc.

Conclusion -

• Use portlet preference for simple configurable parameters
• Don't ever use preference to store information where it would become impossible to do data mining from preference storage because you don't have control over preference storage.