Combination therapy reduces viral load levels in your body, giving your immune system some protection from HIV and an opportunity to recover from the damage caused by HIV.
When people have stopped taking combination therapy, most have found that their viral load increases, eventually returning to the level it was before they started. More worryingly, the immune system starts to deteriorate as well!
If you decide to stop, despite the risks, you should consult your HIV doctor. In most cases, it is vital to stop taking the whole combination on the same day. Stopping one drug at a time or stopping particular doses or just not taking any of them on some days is not advisable, as this will increase your chances of developing drug resistant HIV. If you then want to re-start, you will need to discuss with your HIV doctor whether it is best to use the same combination as before, or to start on another combination.
When stopping some anti-HIV drugs (e.g. efavirenz), it is particularly important to talk to your doctor because of the differing rates at which some drugs are removed from your body.