SAP ITAB INDEX COSTS documentation, setup help and example usage

ARTICLE

Cost of Index Maintenance when Inserting into and Deleting from Internal Tables

Any operations that insert into, or delete from, internal tables come at a certain cost because the index has to be updated. The amount of time needed for this increases proportionally according to the number of lines that remain after the insert or delete position. Any changes you make at the beginning of the table thus require more runtime than changes at the end of the table.
The line width of the table is of no consequence in this context.