Skycap upside: You check-in at the curb, lose the bulky luggage and head straight to your gate.
Skycap downside: They don’t give you a seat assignment, and they cost a few bucks. (Don’t forget to tip; skycaps often aren’t paid a full wage and depend on tips to make their living.)
So when is it best to use the skycaps, and when can you skip them?
First off, if you’re running late, the skycaps could get you onto a plane you’d miss otherwise. If it’s really tight, there’s no guarantee that your bags will make it onto the plane, but I’ve seen some skycaps work near-miracles in this department.
I do it this way: I walk inside the terminal and take a look at both the length of the line for check-in, and the clock. If the line isn’t too long, and I have enough time, I head for the check-in; I get your seat assignments, can make any special requests, get credit for frequent flier miles, and can best address any problems with the flight such as delays or cancellations.
If the line is long and time is tight, I walk back out to the skycaps, tip them well and sprint for the gate. As I mention above, your bags may not move as quickly as you do, but the skycaps will make the effort.
One other scenario: you have plenty of time, but know that your flight is nearly full, and the line is long. Every minute you spend in line is another minute that the window and aisle seats are given away. If you check in with the skycap, then sprint to the gate for your seat assignment, you’ll often find that the line at the gate is much shorter than at check-in, and you’ll actually get your seat assignment more quickly.