Public utilities usually have the right to take an easement by eminent domain. They may be able to compel you to allow the cable on the property but they will have to pay damages for it. Damages include the loss of your ability to use the property for other purposes.
One risk of selling them or giving them an easement is that if you ever need to have the line moved for any reason you will have to pay all costs. For example, if you had to put in a driveway or road or drain that interfered with the line you would have to pay the total cost.
I know a guy that gave the power company an easement to let the lines cross the corner of his property. When he wanted to build a house on the corner they wanted thousands of dollars to move the line.