When I started out, in another century, I played mostly in C. Then I learned G, then F, then D, then A, then Bb, then E, then Eb. I could get by in the other keys, but not as easily because I just don't play them much.
I think in chord intervals, like I, IV, V7. Instead of a G aug, if I'm in C, I think of 5 aug.
I sometimes transpose if a particular song is easier in a different key and I need to sing it in a different key, or if a certain "lick" is easier in a certain key.
For example Floyd Kramer type piano riffs that use his signature grace note thing are MUCH easier in white keys, C,F,G.
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DonM