Why merged cells cause so much trouble, and the setting that gives you the look without the damage

The hostility is not aesthetic. A merged cell breaks a set of operations that everything downstream depends on.

What it actually breaks

• Sorting. A range containing merged cells either refuses to sort or scrambles, because the sort has no way to move a cell that spans several rows.
• Filtering. A merged header or a merged value makes the filter treat the block as one entry, so rows silently disappear from the results.
• Selecting a column. Ctrl with an arrow stops at the merge, so keyboard navigation and any macro that walks the data stops early.
• Formulas and pivots. The value lives in the top-left cell only; the rest are genuinely empty. So a lookup finds a blank, a sum is short, and a pivot rejects the range for having no header.
• Copy and paste into a differently shaped range, which errors rather than doing something sensible.

What to use instead

• Center across selection. In the alignment options, horizontal alignment. It looks identical to a merge across columns and changes nothing structurally. This is the answer for almost every case.
• For vertical grouping, repeat the value in every row and use conditional formatting to hide the repeats visually. The data stays complete and the sheet reads the same.
• For a title above the data, put it in one cell and widen the column or just leave it. Nobody has ever complained about a title that is not centred.

Where a merge is fine: a presentation sheet that nothing reads from, at the very end of the process. If a human is the only consumer, merge freely.