I realise that there are arguments both for and against wearing gis whilst training and I'm not necessarily saying that it's a bad thing but I've noticed recently that at the club that I train at, more and more people have stopped wearing gis to the point where only about 20% of the people at the club where I train wear gis now (me included). Has this happened at the club that you train at? If so, do you think that wearing gis is a good thing or not?
It depends on the context of the art.
If the historic/"traditional" context is important to you, then you should wear whatever gear is accurate and "traditional." If that's the "white pajamas," then wear that. If the art is being studied "just for fun 'n stuff" then it really doesn't matter.
When teaching the Bowie Knife, I have occasionally made students wear leather mocs. It makes you move different because your footing is different. It's an important element to understanding how the weapon was used in its historic context.
If you want to learn how to do gi chokes, a gi (or suitable stand in) is pretty much required. If you're going to do a morote seoinage, a firm grasp on the front lapel is required and a lapel that isn't going to shred is, therefore, a necessity. Try doing morote seo to someone wearing a flimsy T-Shirt.
On the other hand, if you want to practice no-gi chokes & throws, then well, no gi is required.
Ever notice how some "traditional" Asian martial arts have long, skating, footwork? How well does that footwork work in the middle of a field? It's not that that footwork is "wrong" or "impractical" it's that said footwork evolved as an artifact of being able to move indoors on smooth surfaces where short, mincing steps or steps which pick up the feet too far from the surface actually create more opportunity for the opponent.
In short, before you decide if you should be wearing a gi or not or if doing/not-doing so is a good/bad thing, first you must identify what you want out of the art and why you are studying that art.
Peace favor your sword,
Kirk