I see it like this, especially on big pieces…the scab thats forming has no flex. As it starts to seperate from the healing underskin, it cracks from the movement of the body underneath. Sometimes they can crack due to overdrying of the scab, or even because you have oversaturated the area with ointment or even in the shower, thus causing a thick scab to form. If the scab is thick, it will be less pliable, and can crack or get damaged easier. Touchups, are in reality a good thing if your artist gaurentees his/her work, as it insures the brightness and longevity if the tattoo. It also maintains the true quality of the work, and that is a direct reflection of the artist, and I am sure that most of us want our best work out there for everyone to see.