Teamsay
No, you shouldn't be discussing strategies on the field. No assault team discusses strategies or tactics on the field. However, tactics and strategies are practices endlessly so that in the field, they are second nature. (example: everytime you dive into a pool, you don't have to discuss with anyone how to swim, you already know how and it is second nature to you. You just do it.)
Voice communication is definately a huge advantage over keybinds for obvious reasons, but if you pay attention and are aware of your surroundings in a map, key bindings can give you enough of an edge over people who aren't using them. I'm sure everyone knows that key phrases can be bound to one key. In teamsay, it displays your location.....most of the time. Knowing where your teammates are will give you and them a major advantage if you know what to do with the information. So no, I don't agree that you should throw all communication out the window on pubs just because you don't have a voice comm system running for all teammates to hear. If someone calls for backup, look to see where they are and get there ASAP. If you hear "Frag out", stop to see where the frag is going and don't continue to charge into a room that a teammate was trying to clear with a nade. Awareness will make you an effective player. If you are not running a voice communication program, pay attention to the teamsay communications. It will give you bits of useful intelligence.
One thing that I do is to call out my location regularly, on large maps so that if I go down, or take an enemy down, teammates will know the general location of the enemy and where they are attacking from.