I decided to have a look at the base values of quadruple jumps:
http://sk8stuff.com/traindocs/5_levels_perspective.pdf
4T 10.3
4S 10.5
4Lo 12.0
4F 12.3
4Lz 13.6
4A 15.0
There's a big jump between 4S 10.5 to 4Lo 12.0.
The 4F is only 0.3 higher than 4Lo.
There's another big jump between 4F 12.3 to 4Lz 13.6.
Conclusion: It does make sense to train for the 4Lo and 4Lz and skip the 4F (except for completion's sake). If a skater has enough time in his career to learn three different quads, then choose one from 4T/4S, one from 4Lo/4F and the last one will be 4Lz.