i already had detailed discussions about this LW vs RW thing few times. Guardiola is the only coach that used him at LW majority of the time, and it made sense for them considering 1. Robben still being WC on the right, as opposed to Ribery who was in decline for a couple of years already, and 2. Lewandowski (and Muller), whos a monster in the air and can do a lot of damage from crosses. Guardiola also used Coman at RW mostly for that same purpose. also, other than BL i recall only one big game at Bayern where he played LW and did well, the 1st half against us in 2016 in Turin. but ill also add that he played RW the very next game vs us and did even better. on the left, against teams that dont leave him much space, hes easier to shut down. you simply force him away from the touchline and you did your job, as hes not a scoring threat from there because hes one footed. on the right, he can still send crosses to the box, he can cross well with his right when you close him the space to go central and he has to beat you sideline, and has a great distance shot when he cuts in. everywhere else other than Bayern, Costa has been a RW that can also play LW, but it really depends much on what you want from him, who his teammates at CF and the opposite wing are, and whats your playing style. for example, if we add a striker thats not worse than Giovinco in the air, and Max sticks with this lopsided 433 weve been using lately with Cuadrado RB, Dybala RSS and Costa LW, then it makes sense to play him there, as he will have more space there and crossing will be dangerous with a man in the box. this season however, when we played our lopsided 442 with Dybala and Higuain upfront, he made more sense on the right side where he can get in behind those, make long crosses to Mandzukic/Matuidi on the far post, or beat his man to the sideline and make low crosses with his right.