My arguments for facilitating trade-offs among competing programs, if taken to their logical conclusion, suggest that all programs should be discretionary. Obviously, that goes too far. There are good reasons programs should be entitlements. This is good economic policy because the growth or shrinkage of these programs runs counter to what's going on in the business cycle. These entitlements make recessions smaller, shorter, and less frequent.
Equity calls for some individual benefit programs to be entitlements.
An example is veterans compensation. It is only equitable that each veteran with the same disability get the same benefit, whether there is a upsurge in military service or a dramatic decline because of peace. Since this is an individual benefit, the money goes to the beneficiaries irrespective of where they live. Congress doesn't have to readjust regional formulas if the number of disabled veterans grows more in one state than another. The need for long-run planning calls for retirement benefits to be entitlements.