Tosafos discusses the difference between aveilus (post burial) and aninus (pre burial). During Aninus one is forbidden to eat meat and drink wine, and is prohibited in marital relations as apparent from the gemara. During Aveilus one must not wear shoes, and must perform atifas harosh, and turning over the beds (Re: Washing Clothes and cutting hair tosafos assumes that it is assur by both - What would Tosafos would say about bathing during aninus?)What is the reason for the difference?
Tosafos explains that expression of "aveilus" which presumably mean methods of expressing sadness apply only during aveilus, but aninus is more along the lines of distracting one from showing the proper kavod to the meis and from performing the mitzvah of kevurah. One would think that aninus is more of a din in kavod for the meis, whereas aveilus is an true expression of sadness. However, Rashi in Succah 25a seems to assume that aveilus is also only for the purpose of showing kavod for the meis. Although they are both ways of showing kavod, the needs are different. During Aninus the kavod is to be involved actively, but during aveilus the kavod is to express sorrow.