The Exp Share has been a consistent part of the Pokemon series ever since its introduction in Pokemon Gold & Silver. Fans of the older games will know that the Exp Share used to be a device that you could give to a weaker Pokemon to help it level up without subjecting it to battle. Over the course of the series, however, the Exp Share has evolved from being a simple item into a mechanic that gives every Pokemon in your party experience whether you like it to or not.
In Pokemon Let's Go and Pokemon Sword & Shield, whenever one of your Pokemon defeats an opponent and earns experience, the rest of your team also earns experience based on its current level. This could originally be turned off in previous titles, but has now become a key feature in the most recent games, fully integrated into the gameplay.
The trouble with this is that it allows you to essentially ignore half of your team in favor of the other half. Pokemon that level up with the Exp Share will still learn moves and evolve as normal, meaning that these Pokemon barely need to even see battle to become useful. You might think that's fine and dandy, but it actually goes against everything that the Pokemon franchise teaches you, as well as the concept of evolution in general.
From the moment you first step foot into the tall grass, you're taught that what makes a great Pokemon team is friendship. You're often told how the bonds between you and your Pokemon are essential to getting the most out of their abilities, and how Pokemon with ruthless owners obsessed with victory will never be able to beat a team with strong bonds.
Your entire journey with your Pokemon is pretty much one giant bonding exercise. You travel from city to city, collecting gym badges and overcoming tough challenges. However, the Exp Share in the latest games allows you to leave one or two members of your team to just sit in their Pokeballs for hours at a time, and when it finally comes to using them, they're almost as strong as the ones you use regularly. You're not penalized in any way for completely neglecting team members, despite the fact that the Pokemon series has always taught us that the friendship between you and your Pokemon is key to creating a strong team.
I know there are many out there that would argue that the Exp Share is a necessity, and there's a lot of Pokemon in the series that have ridiculously weak starting evolutions - Magikarp is just one example. However, using the Exp Share as an item still has you consciously taking care of a single Pokemon. You're interacting with a Pokemon in your team rather than leaving it to passively benefit from the battles that other Pokemon triumph in.
I might be a little strange when it comes to playing Pokemon, but for me, training Pokemon is a form of attachment. I avoid using the Exp Share for the same reason I avoid catching high-level Pokemon later in the game. I need some quality personal time with a Pokemon to fully consider it as part of my team, and having Pokemon you've raised over the entire game makes the moment when you finally overcome the region's champion all the more special as a result.
The Exp Share in the latest games robs you of that experience. Sure, it makes training easier and helps the game feel less grindy, but it also stops you from growing equally attached to all of your Pokemon. Completing Pokemon Sword & Shield doesn't feel like as much of a team effort as older titles, and the shared experience earned via the Exp Share is a massive part of that.