Just like many composers will start a sketch on a piano, using an ensemble patch is just another tool for sketching and generating ideas. In that sense, it won't hinder your abilities with composing. If it helps you write faster and come up with new ideas and you enjoy the process, then go for it!
However if you wish to also improve skills with orchestration, I would say ensemble patches would hinder your abilities to improve in that area – since effectively it's automatically "orchestrated" for you, so you don't really quite learn the techniques of voicing for various instruments in their ranges (and sweet spots), as well as seeing how the voices in a section interplay. In this way ensemble patches can be misleading because you can't really discern where instruments begin and end (there will frequently be a bit of overlap). Some ensemble patches may also have stuff like octave doubling which is fine but you don't really get a sense of what's going on and when and how to use stuff like doubling as if you were to orchestrate that yourself. And while you may not be at this point yet, but with an ensemble patch you won't really learn anything about how to write divisi vs unison playing for a section, since arguably the entire patch is divisi. If that doesn't make sense to you yet, don't worry about it, my primary point is that ensemble patches kind of do the orchestration in a very broad and general sense to get you started, but you'll eventually want to learn how to do it manually yourself so you can exploit the orchestra to your benefit rather than simply play some chords.
Also, ensemble patches lend themselves toward playing full block chords in a section, which again is totally fine for a sketch to lay out your harmonic structure. However, let's say you want your celli and basses doing a fast staccato bass line, the violas doing some repeating ostinati, your violin IIs doing some slower legato pads, and your violin Is carrying a sprightly melody with different articulations between short and long – such as you might hear in any classical piece for example – well you can't really control or write this way using an ensemble patch. Yes, you could load 5 ensemble patches and play all these onto different tracks, but at that point, you might as well not use ensemble patches as that would defeat their purpose.
So in short - ensemble is fine for sketching; but definitely worth learning to use individual instruments for orchestration and counterpoint etc.
Most importantly, have fun!
