^^ It is not compulsory. You either opt in and work within the budget with greater freedom over what you want to modify/improve; or you opt out of the cap and use your unlimited funding to make improvements in very few areas. Each team would have the option to opt in or out of the budget cap at the beginning of every season. I feel it'd do a lot more good in terms of more teams, reaching out to a wider audience and also more competitive racing..