Agree with what is said above.

A few thoughts in addition to it.

The more defensive walls you have, the harder you will be to score on FKs. If you have 2-3 of them, you can use hard tackling against good opponents without risking too much to be killed on FKs. But I still probably wouldn't recommend it, since the risk of a red card is just too high. I only switch to hard if I am loosing a game.