Add-ons, smart move?

Should you add-on? When would be the best time to add-on? Should you ever do it during a turbo? I know a lot of questions, but i figure there's a lot of varieties of poker.

In my opinion, add-ons are useful during the beginning, maybe the first break. After that, it is inconsequential. It is useful in helping you outlast the donks if you plan to wait.

Speaking in generalities, as long as you have a positive expectation in a tournament, it is almost never "wrong" to purchase a re-buy/add-on. Unless of course you've already spent so much on re-buys that you've turned a positive expectation in to a negative.

I personally set a limit before I start playing, as to how many rebuys I take. Usually if you are above 1500 in chips you can't rebuy. I usually always take the add on.

Add-ons are often better value than the initial buy-in (e.g. twice as many chips for the same price), if so it's nearly always right to take them.

i used to play the 3$ rebuy and instead of treating it as a 3$ mtt towards my BR for BRM, I would treat it as a 9$ MTT since i always plan on adding on once right away and once at break

The others have basically said it: taking the add on, if it's available, is almost always the right thing to do.

Some people suggest that the benefit is only marginal if you're among the chip leaders and it'll add less than 20% to your stack but even then, if you're properly rolled for the tournament then it won't hurt to take the extra chips.