As long as you use your TX.
If you are not going to use your TX for an extended time (months) you shall always remove the batteries regardless of LiPo, Nixx or other.
Take a few minutes to understand the risk. I do keep my lipo in my TX and seldom give it a thought. But, be aware of the risks. Familiarize yourself with lipo safety. Many battery chemistrys may damage you TX. Lipo have the potentially to burn not only your radio but your house. Be safe Be extra diligent like AK says and remember to turn off your radio when not in use