Like the NBA, this avenue really only is available to a limited number of players just based on skill (leaving aside the age limits), but apparently the money in Russia is insane, so if you're eligible and good enough, right now it makes sense to go as early as you can.
There's some thinking on RebKell that overseas leagues are unlikely to pay unless you have the WNBA stamp of approval (interesting, to say the least), which would make it not particularly profitable to leave early unless you can qualify for the draft or you're in the Stewart/Loyd category where everyone knows how good you are.