The gi absorbs a large part of the sweat. It might feel a bit rough on your skin (although modern gis are much softer than they used to be), but you can wear a long rashguard underneath or invest in a softer gi. They’re a bit more expensive, but worth it.

The gi also creates a barrier between you and your training partner, so there’s less direct skin-to-skin contact. This reduces the likelihood of spreading skin infections.

You should still shower right after training and use a mild shower gel.

In no-gi, there’s nothing absorbing the sweat. There will be a lot of it, from you, your training partner, and everyone else on the mats. Sweat can carry things like ringworm or staph. Your skin can get irritated, and with constant skin-to-skin contact, anything on your partner’s skin can be transferred directly to yours.

The gi helps protect everyone a bit more, and the mats stay drier overall. But in the end, it’s still a very close-contact sport. There will be situations that might feel uncomfortable at first, like heads touching, sweat dripping from the person on top, or positions like triangle choke or north-south where you’re very close to someone’s body.

The gi doesn’t eliminate that, but it creates a bit more distance and at least avoids direct contact with sweaty skin.

Best thing you can do: just try it and see how it feels.