What do you mean by decisions? Strictly speaking the senate made no actual decisions, as it was a purely advisory body, albeit one with enormous influence. The Roman state was run by magistrates, especially the senatorial ones (the quaestorship and above), who were duly elected by the citizen assemblies. The senate had some rights to appoint very minor magistrates and could appoint certain extraordinary magistrates, but the senate had no right to pass laws or anything like that. So they didn't really make any "decisions," they gave advice to magistrates, who could do with that what they would. While it was ill-advised for a senatorial magistrate to disobey the advice of the senate it happened anyway, and in the later Republic happened quite frequently. The closest thing to a legally binding "decision" that the senate could offer was the senatus consultum ultimum, which had an influence not unlike a law, but legally speaking was still only advice--a senatus consultum ultimum could still technically be ignored (with horrible consequences, although it did happen) and in terms of status was not legally a law. So what precisely do you mean by "decisions," are you asking about the consulta? If so the relevance of a consultum depended very much on what exactly it contained and how the magistrate it affected decided to deal with it, there's not necessarily a catch-all answer