High pressure:

- Give you better defending ability.
Turn it high when against strong teams, low when you want to save player's condition.

- Give you better attacking ability.
High pressure inscrease the chance your players will recover then ball from the opponent and start counter attack.
Also, you will see your attackers "steal" the ball from their defenders and create scoring oppoturnities.
This is like Gegen-pressing strategy, you can see how it works when watching Liverpool's matches.

Hard Tackling:

+ Improve your defending ability
- Inscrease the chance that your players will get booked, and the opp will have free kicks.

My experience

I always use Hard pressure, even with slightly weaker teams.
If i have good goal advantage, i turn it low to save condition.
Against much weaker team, i use low pressure, still win easily,

I never use Hard Tackling, even against much stronger team.
I turn it hard when i'm the away team in friendly match only (to bring some injuries for the home team)