When a player is assigned to play in a strange position to himself, the chemistry is strongly affected. Independently of his connections with team mates, he will never have more than an individual chemistry of 4, which is very bad. However, it will also affect team chemistry.
If you bought or received a player with a different position from the one that he will play, apply him a position card in order to at least adapt him to a similar position (see the table of similar positions).
On the other hand, if your players already have an individual chemistry of 10, you should not waste coins with position cards. In these cases, they can play in the wrong position that it will not affect their performance.
If you want to apply a card or a sequence of position cards to a player you own, check which option is cheaper: buy the position card(s) and apply it on him; or go to the transfer market to sell your player card and buy another card of the same player but already in the desired position.
The CAM-CM, CM-CDM and ST-CF cards are usually the most popular ones.