This is a really cool way to up your blouse game when you want to look a little different.
Wearing a fancy collared blouse under a long sleeves shirt of some type is pretty common. It can make wearing something a bit more comfortable if the texture on the inside is a little itchy, or it can change the fit of your outer layer. By "wrinkling" the shirt underneath, you can make it look relaxed. By "straightening" the shirt underneath you can make it look super smooth.
There's also the creativity that comes from mixing and matching textures and colors. A fuzzy white tank tops sweater on top of a creamy blue long sleeved blouse is a LOOK.
Here's another way to mix and match blouses with over shirts. Wearing a wife beater with thick straps over a slippy blouse can also be super cute. While a wife beater with thin straps can look super bare bones, ones with thicker straps that almost completely cover your shoulders can look pretty great.
Form fitting wife beaters tend to be made with elastic, giving you a nice form fitting look. It kind of works like a cardigan without buttons, t works best using dressy blouses with muted color tones, like grey black or faded out primary colors.
Long sleeved blouses really allow this style to shin, since they can be drawn through the shirt sleeve loops and pressed into place by the firm stitching.
They can also be used to create a long "shirt dress". If it's long enough and still form fitting, the bottom of the shirt can continue past the hips and grasp the thighs. This gives you a nice hourglass shape and creates the sort of retro quirky dress that reached peak popularity in the early 2000s.