the above post is correct,if you play a c major scale in any order you are still in essence playing a c major scale(and it will sound like c major if there is no harmony/chord,and you will have to "spell out" the sounds of each mode using your knowledge of modal formulas.
you have to look at it from the other way round,as a musician you are in essence given a "challenge"of playing the correct scale over a given chord,the harmony(chords) comes first,even if it is implied harmony(ie just a bass note)
so you need to learn scales/modes so you have choices/options to play,
for example,a -7 chord(minor 7)
minor pentatonic,blues scale,dorian,phrygian,aeolian or any other scale that contains the intervals 1,b3,5,b7(minor 7 chord formula/construction).
if you extend the chord to a minor9 any scale which contains a b9 would not really work(phrygian for example)
also each mode/scale has a particular "flavour"so you start to choose the scale/mode which you think sounds best/personal favourites over each given chord type.
obviously this subject can fill a book so hard to really put in a few paragraphs.
yes but my view/point to this is this is where the mind of a good guitarist comes in rather than blank dots on a 'mode scale chart'
and at any point you have 12 note options to play, and i think people tend to use modes incorrectly
i think guitarists should think with their mind and NOT with dots on boxes of sheets of paper labeled LOCRIAN
a good guitarist can know what they're doing, know where they are and accentuate these modes but to do so by learning them in a way you don't know what they are/how they work- or arbitrarily reading scale charts and not realizing how they're related, probably isn't the best way to go about modes.