cash rate

Is it good or bad practice to include a cash interest rate when backtesting a trading system? If I have a low exposure system then most likely the equity not currently invested would be earning some interest. With a high exposure system it wouldn't make much difference to the results. What do...

G'day people :) with RBA meeting due next Tuesday, any takers on what their cash rate decision will be? IMO, taking into account the recent flood, increase in cash rate is unlikely but, economists sometimes surprise us :D