Am I supposed to be memorising?

I've been playing piano since I was around ten years old, and I've had lessons on and off since then. When I read some of the advice on here, I see people talking about lot about memorising pieces and I'm not sure what this means.

I don't think I've ever memorised a full piece. Sure, I can remember a piece I'm currently working on in general but without sheet music, it sounds pretty bad. Like, I wouldn't remember dynamics and even some things like grace notes or articulations... I've had teachers in the past remind me to work on pieces in small chunks (like 4 bars or so), but I just thought this was just for practising things like getting the dynamics right. For example, I'd combine those four bars and some extra exercises, planning slowly and with intention. Not at all like I'd play them if I were playing through the whole thing.

But should I have also been memorising the whole time too? I'm considering continuing to the last few grade exams, would memorising the whole piece help? Don't get me wrong, I'm not a perfect sight reader, but I think my first ever teacher was such a stickler for sight reading that I never considered memorising my pieces