[Valg]

Assuming the game has a sensible 'hands' system, it would mean that while casting, characters would give up the use of two-handed weapons (quarterstaffs, etc.), shields, or other "off hand" items. This is a game balance decision-- if needed you can always make spells a bit better to compensate for this requirement. (As you would have to do to begin with, because merely requiring a material component is a drawback.)

It would also complicate syntax, which is only a good idea if it achieves a desirable goal elsewhere. Otherwise, in any PvP scenario the best casters will tend to be the ones who are good at configuring their clients to rapidly execute all the needed 'swapping' commands.

Personally, I'd tend towards a system with optional but desirable components-- you may not want players to have to constantly gather/craft items just to do anything with magic, but it makes sense that prior preparation could be used for 'peak' moments. Another implementation might be having some spells require components, and some spells not.