In pretty much any D/s relationship subs are expected to sacrifice power/control, sexual freedom/orgasm control, and privacy/secrecy (among other things) from the get go. These are pretty much anticipated from the start and a sub entering into a D/s relationship pretty much accepts to sacrifice at least this much as it's pretty much what makes up submission. Stricter Dommes will probably require more sacrifices from the beginning whereas more relaxed Dommes may require only a few.
Since reluctant Domme converts may (at least at first) find their lover/sub wishing to make more sacrifices than they would like to accept, I'm not going to include them in the discussion.
What I'm mostly interested are sacrifices that are made during the relationship, after the initial sacrifices have been made and agreed to. In my opinion, sacrifices end up falling into two primary categories and are meant to symbolize two primary things.
1. Sacrifices offered by the sub.
2. Sacrifices demanded by the Domme.
As with any relationship, D/s relationships often have their ups and downs and the sub may find themselves in a position where they have to come up with something special to make up for a previous wrong. A sub may do something drastic or offer up a sacrifice hoping the Domme will see it as being a sufficient display of devotion.
In other cases a sub may wish to make a sacrifice in a romantic way, offering his sacrifice to appeal to his Domme's emotions and use them as a symbol of his love for her.
Both types are thought of in fairly high regard but it is absolutely crucial that the sub's sacrifice appropriately appeals to the Domme's likes and dislikes. e.g. a Domme that loves vaginal intercourse with a live penis will likely be offended if a sub shows up wearing a steel chastity belt and hands her the key saying he doesn't want to be unlocked for the next year.
A difficult aspect of being a sub is that a deep and meaningful sacrifice can often only be used once before it becomes the norm. The result is that the "next time" there must be an even greater sacrifice. I don't think it comes as any surprise that D/s intensity tends to increase over time.
When a Domme demands/requires a sacrifice from her sub it usually has a significantly different feel even though the underlying premises may remain the same. Since I'm prone to giving everything labels and categories, I will say that most Domme-driven sacrifices usually stem from either a test for her sub or a punishment.
A Domme wanting to test their sub may wish to see a symbol of either his love or devotion. Tests of devotion tend to happen much earlier in relationships and tests of love are more common later down the road (often when things grow a bit stale or lazy). "If he is truly devoted to me he should be willing to give up
A sub faced with one of these tests is at a huge disadvantage.
A Domme that wishes to punish their sub may require a sacrifice as proof of devotion and a serious commitment to the nature of the D/s relationship. This is pretty straight-forward and doesn't really need any explaining.
What strikes me as odd is the difference in how each of these are viewed. A sub that offers a sacrifice is seen as loving and romantic. A Domme that requires sacrifice is often seen as "going too far" in the D/s dynamic. What I don't quite understand about this view is that while it's in general agreement that being a Domme in a lifestyle D/s relationship takes a LOT of work to keep things rolling, keep things interesting, and keeping the relationship on the right track, it seems like when I read blogs where a Domme has required great sacrifice on the part of the sub there's often a lot of negative responses both from subs and other Dommes.
I guess the majority of the time I file required sacrifice under "necessary maintenance." Subs tend to get more submissive over time just as Dommes tend to get more dominant over time and rarely do these progressions happen at the same rate. I think that sacrifices tend to serve as a "jump start" to help catch the other party up to whichever one is moving faster along the curve and get them closer to the same page. In cases where this is unsuccessful it's often an easy indicator that the two are not compatible (or not compatible any longer).