Your world ranking directly affects your final place in a tournament. The strength of the fencers in your pool goes down as your world ranking goes up, and so your seed from the pools and your final place should improve.
(This example is based on my very abstract method for predicting tournament outcomes.)
For example, picture a fencer who today can beat anyone ranked 70th or worse in the world at a tournament with a strength factor of 2.0 with 100 competitors. This reflects an attendance of 50%.
If the fencer has a world ranking of 100, he will be seeded 50th going into the tournament, 34th on the first day. There are 84 fencers the first day, which is 12 pools of 7. He will be in pool 10, with the fencers seeded 10th, 15th, 39th, 58th, 63rd and 82nd. They have world rankings respectively of 52, 62, 110, 148, 158, and 196. Since he is able to beat anyone ranked 70th or below he has 4 victories and 2 losses. This seeds him around 29th coming out of the pools, 13th into the DE where he easily wins in the 64 to make it to the 2nd day with a seed of 45th, more or less. As 45th seed he will face the 20th seed, who has a world ranking of 40, and so he goes out in the round of 64, earning 2 FIE points and 200 US points.
Now, take that same fencer and give him a world ranking of 34, not enough for a bye. He's 1st seed the first day, he's in pool 1 with fencers ranked in the world 80, 82, 128, 130, 176, and 178. He comes out undefeated and goes right into the 2nd day seeded let's say 20th. In the round of 64 he faces the 45th seed, with a world ranking of 90, so he wins and goes on to the round of 32, where he loses and finishes around 20th place, earning 4 FIE points and around 800 US points. Same quality of fencing, more points.
This is a simple and very abstract view of what happens in a World Cup. But it should illustrate why your world ranking is important. In that example, with a world ranking of 34th, the fencer gets 800 US points for finishing around 20th. But with a world ranking of 100th he gets only 200 points even though he fences equally well.
In between those two examples, if the fencer has a world ranking between 46th and 93rd, more or less, he can expect to go 5-1 in his pool and possibly be in the top 16 out of the pools. Getting a seed on the second day of 30th or better gives him a bout he can win in the 64, and at least 644 US points. This is a less certain range than the other two, but you can see how improving your rank some will help some, it's not just a matter of being in the top 40.
In this example, the fencer can beat anyone ranked 90th or worse in the world, the tournament has a SF of 1.5, and there are 75 fencers.
If the fencer has a world ranking of 45th or better, he'll get a bye right to the second day, where he can make the top 32.
If the fencer has a ranking of 46th or 47th, he will get a pool where he can go undefeated, and ultimately make the top 32.
If the fencer has a ranking between 48th and 95th, he will get a pool where he will only lose one bout, taking him right to the second day and giving him a bout he can win in the 64.
If the fencer has a ranking worse than 95th, he will lose two bouts in his pool, and make the second day but will have too strong an opponent to beat in the 64.
95th place in the Men's Epee FIE standings right now (November 7, 2002) has 22 points. That may seem like a lot. It takes three top 16 finishes to earn 24 points, or two Grand Prix top 16 finishes. Look at the schedule for 2003 and you see a Grand Prix in Bogota, and one in Tunis, neither of which will be very strong. If on the low side you get 32s at each of those you already have 12 points. Then any two other 32s and a 64 gets you 22 points.
Unless you go to Bogota and finish 8th right off the bat (21 points), it will take a whole season to go from zero to 22 points. Everyone in the top 16 of the US standings has enough skill to do it, if they pick their tournaments appropriately.
Once you have those first 20 points, you build on them the next season, earning more FIE points and many more US points. If the improved ranking helps you make it one bracket higher in each tournament, you will double your FIE points in the second season. After that, no world ranking will help you earn more points, you have to become a better fencer to move up.
From here you can go on to figure out how to Maximize your US Points.