LilyPond scores are indented rather like text paragraphs: all lines except the first are indented by the same amount (
short-indent). This layout constraint is applied in advance and cannot be modified later e.g. on a line-by-line basis.
LilyPond users who need a differently indented line can arrange for that line to start a new score, as in LSR966. That may be a reasonable workaround at a more or less natural break such as a coda, but in general the structure clash introduces severe fragmentation requiring compensatory splicing and fudging. See discussion re LSR966.
This snippet demonstrates the pseudoIndent workaround which superimposes an additional line-wise indentation on the score's unmodified layout indentation. This approach avoids all those score change problems.
There are independent parameters for left and right indentations. It also comes with a freebie parameter for succinct instrument-name modding.