An early desert tile with a Vivarium and a farm (assuming it can get a farm) will produce 2 food 1 energy.
2 food tiles don't help you grow (the growth from that tile is 2-2=0)..... However if you get a 10% food bonus, that 2 food tile becomes a 2.2 food tile... that gives you 0.2 growth where before you had none.
That would still not be very attractive by itself. But there ARE flood plains in BE and combined with farms and the vivarium they could allow a city to grow quite fast, grab a lot of special resources scattered around the desert, mine some hills, and if there is still surplus population the normal desert tiles could yield a bit of additional energy too. Later techs even seem to upgrade farms further. It is a bit dependend on a river flowing through and/or some algae or tuber tiles, but desert cities could be quite effective in the long run.