It's difficult to find any fault with all the advise given above ...... the experts here are the greatest value out there!
I will add the following ...... IMHO ....
TPG add a 'safety factor' to those new to collecting or even those experienced collectors new to a series .....
Here is my own personal take on it .....
I have been absolutely smitten with the Love-Bug for Classic US Commemorative ..... and will acquire the entire 50-coin type set in MS grade even if it takes me 20 years (Lord Willing me that time).
These are very expensive coins ....... can't even touch the low-end at MS65 below $100 .... and many (most) push over $1000!
Sooooo ... for me ..... this is a tough set to research and know 'for sure' the grade of raw coins ...... especially un-certified coins on electronic auctions (read ... E-Bay).
I am doing my homework ..... reading and learning all I can ..... but for now I am relying on PCGS certified coins to start my humble collection ...... which now numbers 5 coins.
You can find me at the PCGS Registry Set #142.

This quest of mine is ... IMHO .... a valid reason to use
TPG ...... filling the gap between knowledge gain and experience ..... for sure in this series the potential cost of a bad mistake will eventually outweigh the premium to buy/certify.
HTH
David
Take a look at my other hobby ...
http://www.jk-dk.art