The Portfolio limit is the maximum amount invested in your portfolio. This amount does not apply to your entire Bondora account, but to this particular Portfolio Pro strategy that you are creating and naming. The Portfolio Pro overview lets you track how much money your portfolio has already invested. It is exactly this amount that you can limit with this setting.
If you want to invest your capital in Bondora using a variety of strategies and limit those strategies to a certain amount, then this rule will help with that strategy. You should view this as a form of risk management in your portfolio.