If it is so obvious everyone knows, and there is likely to be a confrontation because of the tackle, then yes get the card out straight away. Even at grass roots most observers would back you on that.
But for other challenges be careful. Taking aside the expectation of the observer that you follow the correct technique, you sometimes need to give yourself thinking time. Take an example, you see a foul and immediately think red, but then the reaction of the players make you strongly suspect you've seen it wrong (which let's face it, happens to all of us). If you've already got the red card out you are cornered, whereas if they are still in your pocket you have bought extra time. This is why you will sometimes see the top level referees take a long time before actually pulling out the card. They will be talking to their colleagues, but they will also be looking at what is going on around them.
But for other challenges be careful. Taking aside the expectation of the observer that you follow the correct technique, you sometimes need to give yourself thinking time. Take an example, you see a foul and immediately think red, but then the reaction of the players make you strongly suspect you've seen it wrong (which let's face it, happens to all of us). If you've already got the red card out you are cornered, whereas if they are still in your pocket you have bought extra time. This is why you will sometimes see the top level referees take a long time before actually pulling out the card. They will be talking to their colleagues, but they will also be looking at what is going on around them.