ARR is the valuation metric of SaaS. Investors price companies on multiples of forward ARR; "$10M ARR" is the headline number raised at Series B.
ARR vs MRR: same concept, different time horizon. ARR is preferred when annual contracts dominate; MRR is preferred when monthly billing dominates.
ARR growth rate matters more than absolute number for early-stage. 'Triple-triple-double-double-double' is the canonical fast-growth path: 3×, 3×, 2×, 2×, 2× year-over-year.