Definitely the place to start in tournament fishing especially if you don't have a boat yet. You get to learn from some great fisherman(both as a boater and a non-boater), be involved in conservation and youth projects. Involvement can be as little or as much as you want. Most clubs meet once a month.
I enjoy club tournaments as much as larger tournaments.
As a non-boater you get to ride in many different boat which will help you decide down the road what kind of boat and features you might like.
All clubs operate a little differently so find the clubs in your area and attend a meeting to see what they are all about.
Costs vary but for most clubs there is some sort of membership fee. Tournaments run $25-40, plus you have to pay half the gas/oil for each tournament that you fish.($20-30avg but could be up to $50 for travel tournaments)
Some clubs have as few as 4 tournaments and others up to 15.(not mandatory to fish them all)
Most clubs have year end prizes for angler of the year or team of the year plus big fish, etc...
In my area(niagara) you would also need a u.s. license for most tournaments.
Smaller clubs may be 10 people and larger clubs in the 40's

Disadvantages: I don't think there are any disadvantages to joining a club.

Hope this helps.