Quote Originally Posted by 00Able
I aspire to pick up this knowledge
I'd draw your attention to the below:

Quote Originally Posted by Rita Mae Brown
Good judgment comes from experience, and often experience comes from bad judgment
That's how most people learn that SUMPRODUCTs & Arrays are bad news when used in large quantity and/or with large precedent ranges and/or in Volatile manner.

Quote Originally Posted by 00Able
performance is always of interest and I am afraid that is one aspect that I do not fully understand...volatile excel functions...someday I'm hoping I will
Check out the Volatility link in my sig. - and in fact read through the whole site in full - it's the best resource on Excel performance & optimisation re: calculation engine etc...
(the author Charles Williams is an MS Excel MVP and has written white papers for them on the same subject - covering a lot of the same material)