I saw a video in youtube where they told us to play only the bottom 3 strings while upstroking and all 6 strings while downstroking. The reason given was that the upstrokes will sound slightly higher pitched compared to all the downstrokes and that difference makes it sound good. (Of course which strings we actually play depends from chord to chord, but in general this is the recommendation that was given).
Since I am new to playing guitar I don't know whether this is the correct way to play or not. Is this a recommended way to play the upstrokes?