A large opening repertoire
- takes longer to build in the first place
- needs to be memorized and recalled during games
- is more prone to errors in evaluations of critical positions, and as computers get stronger – needs to be periodically reassessed
- may become useless when chess fashion moves to a different direction, and everybody stops playing those “sharp popular lines”
- is more difficult to maintain and update over the years, even if it is digital
While you hope a larger opening repertoire gives you more flexibility, usually the reason your opening files grow large – is because your favourite opening lines give opponent a lot of options, and you have to consider all of them in your preparation. The key to making it manageable - is to limit those options by finding early but solid deviations that you are comfortable with, striking a balance between playing sound lines, and not falling into your opponent’s favourite variations.