When line numbers are displayed in the gutter, a 5-digit width is always reserved for them, even if the buffer has less (e.g. 20 lines) or more (e.g. 200,000 lines). For a buffer with 20 lines, there will be redundant space reserved for the line numbers. For a buffer with 200,000 lines, the line numbers will be written on top of the fold markers. For a buffer with 2,000,000 lines, the first digit will be "cut" by the gutter boundary and not be completely visible.