The advantage, or disadvantage of lapping depends on what you are trying to achieve.
For a slightly rough bore, lapping can help, but you need to remember that lapping will only remove about .0005" over an hour, or so of work, so lapping won't remove pitting.
If you have a new gun that is cutting patches, lapping can help, as can swabbing the bore with a green scotchbrite pad.
Cut a 1 1/2 inch square of green scrubbie, and using a jag for the next bore dia smaller than your barrel, scrub the bore about 50 strokes.
Oil the bore well prior to scrubbing.
God bless