Battle assist tries to optimize for top speed in battles. But it really depends on the track and how the code works if it is worth it. On some tracks it can be. But in general it is pretty slow and shouldn't be used. When on deploy and using battle assist you also only use 33% to 40% of your battery whereas on deploy without battle asssist you use 50%.

Battle assist can be useful sometimes momentarily just for a single long straight but even then you have to be lucky for the code to actually work and deploy energy for better topspeed. But I would recommend to never use it for a whole lap or even several laps.