Personally, any guide is just a starting point no matter where it is at or who it is on or who it is by, it gives you a starting point of how to play, but that will never take away your own personal flavor to certain champs, it's all about whatever feels best.
This is the easiest example for me i can give, When i started playing Yasuo, i looked up so many guides and tried them all, heres the cool thing about guides, they allow you to learn cool tips and tricks for champs, so that's what they are REALLY for, runes and mastery's are all up to you however, for one, i see most yas guides have life steal quints, or some form of early movement speed or attack speed, and i just roll flat AD damage, and armor/mr for defensive. The AD marks and Quints give you minion execution power and also allows for a huge E, Q hit, and i found through trial and error, that that is what works the best for me despite what the guides tell you to do.
So what you should take from this is, learn the guide thoroughly, but still find what best works for you, who knows, maybe every bit of the guide will work for you, maybe some parts, etc, but always learn all the tips and tricks they have, you never know when someone might find a new one, but always experiment and find what parts work best for you!
And iv'e noticed that pro player guides are often not intended for normals or even ranked in some cases, which is why i use community made ones on MOBAFIRE, and then adapt my own style from it and find what works for me.
Find what works best for you m8, and GL