The answer partly depends upon what nutrients you may already have, from the tap water, organics (fish load, fish species, fish foods used) and the type and number of plants.
Aquatic plants require a balance of 17 nutrients. Some are more important than others (macro-nutrients versus micro-nutrients), but all have to be present (available to the plants) or photosynthesis [growth] cannot occur, or it will be slower, depending upon what is minimal or missing.
Flourish Comprehensive contains all but 3 of the 17 nutrients. Those not included are oxygen, hydrogen and carbon. These three normally occur naturally in the aquarium, so there is no need to be dosing them. Except for increasing carbon, as one does in high-tech methods, but we can ignore that for the purpose of your question.
Flourish Trace contains only the micro-nutrients. You can see the list and the proportion on the Seachem website, here: Seachem. Flourish Trace
As they state, Trace may be used alone or with Flourish Comprehensive. As I mentioned at the outset, some nutrients may occur in your source water, and some certainly from organics, but I doubt any source water (tap water or well water) contains everything or even sufficient quantities of some, making it necessary to add them either as liquid or via the substrate.
I use only Flourish Comprehensive. It contains all those trace elements along with the macro-nutrients too. I have not experimented with adding Trace as well, simply because I am getting what I consider excellent growth from just the Flourish comprehensive, and I see no point in spending money unnecessarily. However, if I were to use Trace in addition to Flourish Comp, it may well be that my plants would respond even better. Next time I'm in the fish store I may look for a small bottle of Trace. Your question has intrigued me.
So, to recapitulate the response to your direct question, I would find out what is in your tap water and then either continue with Flourish Comp on its own, or try Flourish Trace. If you'd like to provide information on your tap water, or a link to the water supply site that does, I'd be happy to take a look and offer my opinion. I know that in my case, there is nothing in my tap water in the way of nutrients and I absolutely must use a Comprehensive to supply the macros.