I hate when people use merge cell in excel, particularly when it’s in a calculation sheet. It kind of take your cursor somewhere else while using keyboard shortcuts. I believe if merge cells are used only for presentation purpose then it’s okay else big NO.
One good alternative that can be used instead of merge cell is format cell->Alignment->under horizontal option select center across selection -> OK
It gives the effect of merge cell without actually merging them. It makes a lot easier working in calculation sheet.