Value of Rec Letter(s) for MBA Admissions?

I'm currently in undergrad and I've heard of the necessity of getting letters of recommendation from professors/advisors, as these will likely prove valuable when applying to graduate business schools.

For anyone who has attended graduate business school, or perhaps other undergrads in a similar position as mine, how important are letters of recommendation from professors when going through the MBA admissions process? If they are indeed important, is there an ideal amount of letters? Any other relevant info? Thanks!