It's best to move furniture away from registers during the heating season. This is especially important with baseboard heat where it needs to draw cooler room air up under the register and release it from the top at toasty temps.
To help keep furniture from sliding back up against the registers from normal daily use - use a small board (perhaps 1/2 thick by 3 inch width) cut to about 6 or so inches in length. I like to use pine scraps from my workshop and if they will be visible, I apply a coat or two of poly so it blends with our wood floors.
Simply place the wood behind each furniture leg and tuck it under the register or push it against the wall. This way the sofa, bed or table won't be able to get any closer.