There are many reasons as to why you might choose to add extra supportive insoles into your shoes, and it can be a very good idea especially if you suffer form conditions such as flat feet, high arches or your feet over pronate or under pronate when you walk or run these conditions make it more likely that you end up with injuries such as Plantar Fasciitis or even Achilles tendonitis (due to inflammation of the Achilles tendon which connects to the plantar fascia) this is because these conditions means that your plantar fascia (arch) of the foot is tighter than usual and can become more easily inflamed under tension and pressure. The extra support insoles can provide can help release some of the tension in the plantar fascia.
Having too much arch support can be bad but having the right amount is good. Too much arch support is often is a real problem when wearing custom made insoles as they leave no room for your feet to support themselves thus weakening the supporting muscles around the arch. The purpose of arch support insoles really is to help align your foot in a comfortable position helping to stabilize your foot and body, ease tension and pressure away form the plantar fascia of your foot, absorb and spread shock and pressure from unusual forces that would otherwise damage the foot and to help encourage positive bio-mechanics and function the foot.
Your feet do need extra support when doing sport, but not in the way you might first think of. Support in the form of stabilizing the foot and correcting footing and improving balance all helps to improve form and technique in sports from jumping to running.
Custom insoles have been found to weaken the arch of the foot but not all insoles are bad. Make sure you buy some that give your feet room to maneuver, look for insoles made form gel as one of the main purposes of insoles is to help dampen the effects of shock whilst running and to spread the pressure that can build up in places such as under your heel and gel is the best and most adaptable material to do all of this. Gel insoles will offer support and stability which also adapts but the gel does not over support unlike fixed custom insoles that do not adapt this means that your feet have room to move and support themselves. this can all seem a little bit confusing and daunting especially when looking on the internet for the first time about insoles and finding that much of the information you read contradicts other information you just read before... so If you are still unsure about the types of insoles you can buy and the differences between them here is a good article.