I haven't yet bought a 3 exchange domain, but I presume that one strategy is to take out the snap on a domain that might have quite a bit of competition, second time a slightly less attractive domain, and if you are unlucky enough to have to use the 4th try, go for a domain that there is very little competition, even if only to recoop a normal registration fee. (or tell yourself that it is worth the risk going for a more attractive name if your chance of getting it is 30% or whatever).
But as I say, I have no experience with these snaps.