I think the advantages/disadvantages question depends on alot of things, but I'll say that "if" done correctly that their are advantages and if done incorrectly their are disadvantages. Correctly done, your fretboard will be clean, feel good on the fingers, promote longer string life and long fretboard life. Incorrectly, or not at all, and you can have alot of different problems, sticky, dirt collecting, stings go dead quickly, overconditioning with the wrong type of oil/etc, can cause those type of problems and if done long enough, given the right conditions could even cause the fretboard to swell enough to start pushing the frets up, not conditioning in a really dry climate could even lead to a fretboard developing a crack or cracks, and when it does you got some major trouble. Remember that unsealed/unfinished wood (ebony, rosewood fretboards) never loses it ability to absorb or lose moisture, wood fiber is like a bundle of soda straws, it absorbs or loses moisture best thru the end grain but because of the way grain runs thru wood and the way we cut it, some of that end grain is exposed even on the face of a board, if wood swells or shrinks too fast, it cracks, because the exposed outer surface moves faster than the unexposed surface,( thats why alot of accoustic guitars develop cracks in their tops) the tension has to be relieved and thats why it cracks. To a certain degree, conditioning the fretboard acts as a sealer for the fretboard to slow the process of absorbtion/loss of moisture, which can even be one factor in the need for the seasonal truss rod adjustment alot of us have to do. I guess their are alot of factors that could come into play, and I know their are exceptions to the rule, but a guitar is alot like a car, clean and well maintained usally means years of happy service, left to the effects of time, the elements and abuse, the service life will be greatly shortened, and thats all I have to say............