If the offence is an obvious caution then it shouldn't be managed, I agree, but there are offences which may not be 'obvious' but are still cautionable or not cautionable depending on temperature of game and a few other factors for which a referee may wish to not issue a second caution, but they may issue a first.
Nobody is going to thank you long term for sending a player off for a questionable SPA off the back of a genuine attempt to win the ball, but if you've got a situation where one team have had 3-4 cautions, the other have not had any, the team who has had one is leading and the same 'questionable' SPA occurs, you may choose to caution for it to aid your match control.
Edit: When I say questionable I mean not necessarily ticking all the boxes for SPA but still has hints of SPA.