Why Less Is More When it Comes to Opening Repertoire

Garry Kasparov was notorious for claiming that during his most productive years as an opening researcher, his database of theoretical analysis grew in size by many megabytes. I would not be surprised if these files gave him a competitive advantage over many opponents. For a mere mortal, however, these megabytes of analysis are likely to be a burden for many reasons.
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.