Following the financial crash, lenders have broadly been able to repair their balance sheets. But for established lenders, cracks have appeared in their business models. Margins are shrinking. Rock-bottom interest rates have pinched profits, new regulations have jacked up costs and a host of nimble competitors threaten to chip away at their businesses. Big banks spent the past five years wading through regulatory reforms. Now a main battlefield for banks is how they can squeeze profit growth out of lower-cost operations and put their balance sheet to work.