There are several benefits of blade servers, but they depend on how many blade servers you have and what your needs are.
Blade servers allow for a single management platform. In the old days, patching 10 servers was challenging and time consuming. Blade servers make this much easier -- you can administer several servers within the same chassis without having to move cables or change KVM switch settings. They also allow for faster server-to-server communication, since they share a wire speed backplane instead of a network. Wire speed means that functionality is in the hardware, not software, and is faster.
People often overlook labor in their calculations for return on investment and total cost of ownership. The break-even point for a blade server is when you replace four regular servers.
More on blade servers:
What to know before you buy
Blade server pros and cons
Important factors to consider in your purchasing decision
Virtualization hits blade servers
How server storage space affects blade server virt?