I did not find an example, but I heard from another poster that two RA can be handy for implementing something called 'milli-code' routines. I suspect its a case of infrequent usage, but a real pita not to have two regs available. Many RISC type designs allow a GP register to be used so there is more than one register available. PowerPC for instance allows branching to the count register in addition to the link register. I suspect the count register doubles as a second link register sometimes.