The mesh top earns its spot the evening you want to look like you made an effort without actually doing much work, layered over a decent bra or a cami, under a jacket you'll take off the second it gets warm. It's the thing I reach for when a plain top feels too flat for the occasion but I can't face anything structured.
Before you buy, hold it up to the light and check how see through it actually is, because mesh ranges from barely there to practically a net curtain, and the online photos always flatter it with careful lighting and a strategically placed arm. Check the weight of it too, some mesh has a bit of body and sits away from the skin, other stuff clings the second it meets any warmth. Look at the neckline and hem for how they're finished, a raw or heat sealed edge that's starting to fray at the seams on the hanger will only get worse. And check whether there's a scalloped or raschel pattern versus a plain open weave, because the patterned ones hide a lot more and read less like underwear accidentally on display.
Be honest about where it falls down. It's not for anything where you need coverage without a second layer underneath, so don't buy one thinking it'll double as a top on its own unless you're wearing it with a slip or bralette you're happy for people to see. It's also not brilliant in true heat despite being lightweight, because sweat shows through mesh in a way that's not flattering, and it's not forgiving on anything with texture underneath, every seam and bra strap announces itself. A well made one has a proper weight to the yarn rather than feeling flimsy and static prone, stitching that doesn't pucker at the shoulders, and a finish that doesn't catch on jewellery or nails the way cheaper mesh does within a wash or two.
On sizing, mesh has some stretch but not much structure, so go by your usual size rather than sizing down for a tighter look, which just strains the weave and makes it see through in places you didn't intend. Watch the shoulder seams, they should sit on the shoulder rather than halfway down the arm, and check sleeve length against your wrist because mesh sleeves that stop short look unfinished in a way that cotton gets away with. A top that bunches at the underarm when you lift your arm is one to put back.
Get the layering right and it's one of the more useful odd looking things you'll own.