1) Each piece can be worn separate from the others, giving you a vest with a blue blazer or under a leather jacket, trousers with a sweater, and the jacket with jeans. Especially in the more modern trim cut models.
2) The newest tweeds aren’t the bullet-proof stuff that used to stand up on its own. they are lighter, more wearable and less constructed — making a full tweed suit more comfortable — while still standing up to the many winters to come.
3) Tweed was developed to help hunters blend into the local hillsides. You’re essentially wearing a stealth suit of camouflage.