According to your experience, what are the advantages/disadvantages of using 1 or 2 more carriers?
The advantage is that you have more reserve planes, which is especially useful in the initial battles with enemy Carrier groups since both sides see heavy plane losses normally. By bringing 1-2 extra Carriers you lose a bit of airstrike power, but gain an upper hand in shooting down all enemy Carrier planes.
If taken to the extreme it is quite popular in Multiplayer to put only fighters on the Carriers, and put all your Carriers in a single fleet, for the first battles with the enemy fleet and keep this configuration until the enemy run out of replacement Carrier planes.
I have read in many posts, that for fleet-in-beeing and trade interdiction it is supposed to use 4 carriers / CAG and for Base strike 6 carriers /CAG is suggested.
I believe that most of those posts are based on the misunderstanding that the overcrowding reduction impacts how many Carriers you can bring without penalty ( which is wrong ).