Raising Capital can be for many different reasons. Your total borrowing with the lender will generally be 80% of your property value at the maximum, although there is the odd lender that will allow up to 85%.
The most common reason to borrow more is for Home Improvements but here are some other reasons;
Other properties - Buy to Lets/Holiday Homes
Paying for Education
Deposits for Children - Bank of Mum & Dad
Divorce Settlements
Repaying Equity Loan on Help to Buy Scheme
Generally the only thing lenders don't like you to use the money for is for Business Purposes but their are specialist lenders who would help in those situations.