There are a number of issues.
Mechanically, that means fewer places to put enchantments. There was already one such reduction between Morrowind and Oblivion (one could wear standard clothes beneath armor and high quality clothing could hold a very good enchantment). While I prefer (from a style standpoint) to wear a unified look on my characters, I generally stay away from the many quality one piece armor sets the modding community made for Oblivion simply because they offer less flexibility when it comes to how badass my character is in the end. This reduces my ability to tailor my character on the fly fairly significantly. It also gives me fewer options when it comes to wearing the armor. For example, at high levels of skill, I can get enormous protection (e.g. max) from a helmet, shield and chest piece. This means I can choose to wear other armor parts because of how they look or how much they weigh rather than for how much protection they confer.
Cosmetically it makes a difference simply because people (not me generally) want the ability to mix and match. Much of the Oblivion community at this point seems to regard the game as an interactive doll design program. There are animation packs that give new poses, "armor" that is purely cosmetic, new races that do little more than shift a character look towards some fetish etc. There are also those people who just want the option of taking a cool chest piece and pairing it with cool greaves that aren't from the same set.
Mechanically, that means fewer places to put enchantments. There was already one such reduction between Morrowind and Oblivion (one could wear standard clothes beneath armor and high quality clothing could hold a very good enchantment). While I prefer (from a style standpoint) to wear a unified look on my characters, I generally stay away from the many quality one piece armor sets the modding community made for Oblivion simply because they offer less flexibility when it comes to how badass my character is in the end. This reduces my ability to tailor my character on the fly fairly significantly. It also gives me fewer options when it comes to wearing the armor. For example, at high levels of skill, I can get enormous protection (e.g. max) from a helmet, shield and chest piece. This means I can choose to wear other armor parts because of how they look or how much they weigh rather than for how much protection they confer.
Cosmetically it makes a difference simply because people (not me generally) want the ability to mix and match. Much of the Oblivion community at this point seems to regard the game as an interactive doll design program. There are animation packs that give new poses, "armor" that is purely cosmetic, new races that do little more than shift a character look towards some fetish etc. There are also those people who just want the option of taking a cool chest piece and pairing it with cool greaves that aren't from the same set.