How Important is Weapon Proficiency?

[Jenrock]

As a fun bit of player-involved world building, I'm thinking of making a change to the Unearthed Arcana weapon groups. Character still receive the same number of weapon groups (basic+4 for fighter, etc), but the difference is that the players define their own categories.

My game has an Asian bent (though this would be applicable regardless) and I want each group to represent a style or part of a style. A Paladin who practices Hammer of the Gods, for instance, might choose a collections of blunt weapons, whereas a Rogue who practices Steel Bastion might emphasize weapons that could be used in conjunction with a shield.

I like this idea because it involves the players in world building, and because it turns nonproficiency from (in my opinion) "I don't know which end is up" to "I use the hammer like I would my sword so that I can utilize my Deft Hunter style."

How much should I care about the players' weapon selections? Ostensibly, martial characters would benefit the most, and I don't see that being a problem. What repercussions am I not considering?

[OldTrees1]

It boils down to how much realism you want.

Are Cabers and Needles allowed in the same group?
Shortbows and Greatswords?
Handcrossbows and Rapiers?
Hammer and Swords?
Various Slashing Blades?
(ordered from extremely permissive to permissive)

[Jenrock]

While I'm not too concerned about realism, I will either want the styles to have cohesion, or my players to have a really good reason why they don't. That being said, realism allows for some degree of amalgamation of various weapons into a single style. While my knowledge is less than excellent, it is my understanding that The Flower of Battle has instructions concerning the lance and sword in all its folios, as well as instructions concerning the poleaxe, dagger, and grappling in some folios.

Cabers and needles - Not unless they can make it awesome.
Shortbows and Greatswords - I can see how that might work.
Handcrossbows and Rapiers - This would make sense for an urban style.
Hammer and Swords or Various Slashing Blades - Sure, why not?

[OldTrees1]

Since each character will have multiple weapon groups, I would suggest having the weapon style be the combination of weapon groups. Not only are the resulting weapon groups more cohesive, but this works for broad weapon styles (3 groups/style) or many specific weapon styles (2 groups/style)

Honestly, since monks seem like they would know multiple styles, you might want to increase their weapon groups from 1 to 3

[Jenrock]

A strong point, and one I was beginning to consider. I think that probably does make the most sense.