The downsides of a skeg are:

1. added weight, about 3 pounds
2. added expense, about $200
3. lost storage space, which is important in smaller boats
4. added maintenance: skegs need more work than any other part of a kayak
5. potential leakage problem: as cable has to run through the boat it greatly increases possibility of leakage
6. can be unreliable: needs to come from a manufacturer with high quality and one that will stand behind problems.
7. some skegs are hard to operate in rougher conditions

The upsides of a skeg are;

1. a skeg makes it easier to control the boat in rougher conditions (not needed in calm conditions)
2. adjusts for a slightly untrimmed kayak
3. compensates for poorly designed kayaks or unskilled paddlers

While the number of negatives outnumber the positives, the improved control in rough conditions is very important and for many people will outweigh all the negatives.