Many companies use the Uptime Institute tiering system when planning to build or lease enterprise data center space. Companies ask vendors if they are a tier III or higher data center. What these companies are often concerned with is the uptime level they can expect from the vendor. If you consider data centers with 4 1/2 9's (99.995% uptime), you're getting 36 minutes of downtime per year or less for your production systems or your disaster recovery center. If your using an outsource data center that is a 99.995% uptime facility, you may reap the benefits of lower capital costs over time. You can also leave the worries of redundant systems and concurrent maintainability to the data center professionals.
If your cost of downtime isn't high, you probably don't need to be in a 99.995% or Rated-4 data center. It may be cheaper to keep your systems in-house or in a lower tier facility. But 99.995% uptime data centers are not always more expensive than lower uptime data centers. Compare options. Affordable colocation doesn't have to mean more risk of downtime.