MBP: what apps/activities require discrete graphics processor?

Hi - I want to buy my first Mac - a Macbook Pro. I like the portability of the 13" because I travel a lot in my job. I have a corporate laptop but I will ditch it and use the MBP for office duties.

At home in the evenings though I will connect the MBP to a 24" widescreen display and use it for everything from browsing the web and watching divx through to editing HD movies from my camcorder and processing RAW photographs in Lightroom. If these will benefit greatly from the extra graphics processor you can get in the 15" model I will go for that instead and learn to live with the larger size/weight.

Ideally i am looking for a list of apps and types of apps that need or benefit greatly from the extra graphics processor. There may be something I see that i have not thought of yet and may want to do in the future...

As mentioned before my real concern is not cost - it is weight/size. I would prefer the 13" but definitely don't want to be locked out of using the Mac for certain activities because it is missing the discrete graphics processor.

Hope you can help a complete Apple noob.
Dub

 

Could you expand on your answer? I am not sure what you mean.