* Last time around, the SNP were slightly closer than the Greens to preventing UKIP from winning a Scottish seat. An extra 32,100 votes for the SNP would have stopped UKIP, whereas the Greens would have needed an extra 32,230. That history lesson isn't strictly relevant to today's election, because the Brexit Party appear to be stronger in Scotland than UKIP were five years ago, and are probably guaranteed at least one seat. But I did hear last night that someone was planning to 'tactically' vote Green, specifically because of their mistaken belief that the Greens were closest to denying UKIP in 2014. So it's probably just as well to put the record straight.
* It's essentially impossible to cast a tactical vote under this particular electoral system. The only limited exception to that would be if you're planning to vote for a very small party (such as Change UK) that has no realistic hope of winning a seat in the Scottish electoral region. If so, you're probably wasting your vote, and you might be better off switching to a larger party. But apart from that, to make a sound decision to switch tactically from one party to another, you'd need to know in advance exactly how everyone else is going to vote, and that knowledge simply isn't available. The best proof of that point is the fact that three different pro-Remain "tactical voting" websites have managed to come up with three completely different and contradictory recommendations for Scottish voters: one urges a vote for the SNP, one backs the Lib Dems, and the third plumps for the Greens. It's just glorified guesswork. (And in the case of the website recommending a tactical vote for the Lib Dems, there may well be an agenda behind it.)
* A low turnout will almost certainly favour the Brexit Party, so the one and only reliable way of making things harder for Farage is to persuade as many of your pro-indy family and friends as possible to actually vote.
* There is no ceiling of support above which any party won't need more votes. Many polling subsamples have put the SNP in the high 30s, enough to win three of the six seats. But, because of the way the D'Hondt formula works, there'd also be a chance of a fourth seat with a few extra percentage points. Of course there's always a possibility that the polls are overstating the SNP, in which case a fourth seat would be out of reach - but, if so, the SNP would still need votes to ensure they win three seats rather than just two. There is no scenario in which they won't need as many votes as they can possibly get.
* If you want to help generate momentum towards an independence referendum, a vote for the SNP will have a bigger impact than a vote for the Greens. Today's election will have no direct effect on the independence campaign - it's purely psychological. And that being the case, what matters is how the media report the result. The London media in particular are probably only dimly aware that the Greens are a pro-indy party, which means that a Green seat will be interpreted primarily as a victory for left-wing politics and environmentalism. By contrast, every SNP seat will be reported as a direct endorsement of an indyref.