Servers don't use more electricity than any other desktop so I wouldn't worry about it.
My company leases/rents 10 servers so that we don't have to mess with them if one breaks. If needed, they can take the hard drive out and place it in another machines in less than an hours.
About every 4 to 5 years we replace the servers with brand new ones at no cost to us. We generally get a better machine at a slightly lower monthly cost.
We can also return/stop using a server at any time and don't have to worry about losing a lot of money trying to sell one.
And as you've mentioned - there is no upfront costs when you rent.
On the other hand - if you own the server, you'd save a lot of money provided you didn't need any repairs.