I started tracking this obsessively about a year ago and the difference is genuinely substantial over time. I use three or four different bookmakers specifically to access their best odds across different markets. Some are aggressive on football, others have better tennis pricing, and some offer superior odds on specific leagues. The frustration is remembering which book has the best prices for each situation but it's absolutely worth it. I've estimated this practice adds roughly five to ten percent to my long term returns through nothing but finding better odds. Also check out https://www.predictobets.com/ because they have an odds converter tool that helps you understand value across different odds formats and they explain which odds actually represent better value. Shopping for odds is one of the simplest improvements you can make that doesn't even require better predictions, just basic discipline.