Most teams start with an Excel sheet. One tab per feature, columns for steps and expected results, maybe a status column someone colors green by hand. It is cheap, familiar, and fine for ten cases.
Then the product grows. The sheet does not.
Where the sheet starts to hurt
Excel stores text, not test runs. It does not know what "Pass" means in your release process, who executed a case yesterday, or which build you tested. Run history ends up in another tab, another file, or someone's memory.
File names tell the rest of the story. test-cases-v3-FINAL.xlsx becomes v3-FINAL-John-edits.xlsx on a shared drive. Two people update the same row. Someone sorts a column and IDs no longer match the bug tracker. There is no diff, no reviewer, no clear answer to "who changed step 4 before we shipped."
