In case you never knew it has a name or thought it was a screen distortion, that ‘blobby’ bit in the bottom right hand corner of a cell is the AutoFill handle.
When you hover over AutoFill, the cursor turns into a black plus.
When you click and drag the AutoFill handle, sequences may be created, or data/formulas copied.
However, did you know when you double-click the AutoFill handle, your sequence/formula will fill down as far as the last row of data to the left of the current column (row 13 in the example below)?
If you have thousands, or tens of thousands of rows, the sequence/formula will be filled to the last row of data.