The winner of this match will play WI and the loser will play England, we know which team everyone would rather face. However, even if Pak/SL loses this you will expect them to beat England and would likely to face Bangladesh in the semi-finals. I think if Pak/SL wins this, they will face WI next match but will have to face India in the semi-finals. Now they have to face one of the favourites in the semi-final but the best option would be to win today, and beat WI rather than losing today and beating England.
SO it is
1) Win today, beat West Indies and face India in the SF, India are the best team in this competition
2) Lose today, face England and beat them, face Bangladesh in the SF. Now that is a big NO-NO because if you lose today, you not only lose confidence and momentum but you face two tougher teams - England/BD compared to WI/India. Keep in mind, BD are hosts and it will be tough because for the first time in their life they will be cheered against by a crowd.
So yes, in a way this is a very crucial match for both teams. Win today, WI are an easy team to beat no offence and then go on to face India with full momentum. You definitely don't want to face England with red hot form nor do you want to face BD on a jam packed stadium.
Its really confusing as to who faces who in the semi finals....Some places say winners of QF 1 play winners of QF 2 while some say QF 1 play QF 4! I personally think its India Bangladesh in the semis as thats what was stated initially stated.