Grappling with a gi on does allow you to use it to grab on to, choke with the lapels and also learn to defend against those same techniques.
However, while the pants make be about the same material-wise, shirts may be a lot different. Gi jackets are somewhat loose, make ing them easy to grab, and also don't stretch, making them easier to use for control. BUT, nobody I know wears a gi outside of the dojo. T-shirts and sweat shirts are stretchy, so may not allow for the level of control you are used to. And tank tops are particularly difficult, as there is really no fabric to grab onto.
I really dislike it when students train in T-shirts (which we allow during the summer) because it is much harder to practice several of our takedowns which rely on grabbing the clothing.
So, it does make sense to do at least some practice without a gi.