When you create an opportunity you can define its potential worth either as a fixed bid or lump sum, per hour, per week or per month for a certain time period. This allows you to quantify how much upcoming work you think you might have in the future, and allows you to plan for that eventuality. You can set a probability of winning the opportunity out of 100, and a forecast close date for the deal to happen. You can also choose a category to put the opportunity into (eg: product sale, maintenance contract, or commercial large sum donation) and set permissions on who can see the opportunity and who's responsible for it.