In the tarp vs tent debate there’s the usual fixation on weight but there’s also effective usable space to consider.
We’ve a Terra Nova Lasercomp, it weighs 900g and is at best a 1 man tent but you can squeeze two inside if they are good friend or are married. If you do that you can’t use inflatable sleeping mats as they take up too much space and the walls of the tent start to hem you in – it’s bad enough just one person when using an inflatable mat.
Compare with something like the Alpkit Rig7, weighs 550g but add poles and pegs and you are looking at 700g. There’s actually masses of room for two and with a bit of careful pitching you could get three under it. If it was midgey then our bivy bags which have built-in anti-midge panels are 170g so that’s 1040g.
For 140g extra the tarp is much more usable, particularly for two people. It and the bivy bags take up about the same space as the Lasercomp (I’ve not done a direct comparison.) If I was on my own then the tent becomes a valid option.