When you are dealing with customers' data, security is a major concern. You need to make sure that your data in Zoho CRM is not accessed from an unsecure network. You may even prefer that your employees access CRM only from the office. You can also restrict, logging in to and using Zoho CRM to specific IP Addresses only.
With the Allowed IPs feature, an administrator can add the IPs for individual users or for users in a specified role or a group. Users can log in to Zoho CRM only from these allowed IPs added by the CRM administrator. This also applies to all the other Zoho products. So if you are not able to access Zoho CRM from a specific IP, say your home office, then you will also not be able to access the other Zoho applications like Zoho Mail or Zoho Docs.
Existing CRM accounts where Allowed IPs is already configured can continue to access the feature from Setup > Users and Control > Security Control. However, if allowed IPs is disabled, then you can enable and access it only from the Zoho Directory. Read more about Zoho Directory here.