It's memory space, TfL recently said that there were 16.5 million dormant Oyster cards out there with just under 30 million pounds of credit on them. No computer system really wants to have to remember 16.5 million details on its active servers if it can avoid it. So dormant accounts are moved off the active system.
Cons: A £7 cost applies when you get a standard or visitor card. You'll need to top it up in advance of travel. You can't use an Oyster card at any station between Reading and Iver.
If you only have pay as you go credit on your Oyster card, you can lend it to someone else. Two people can't use the same contactless or Oyster card for a journey. If you have a Travelcard, Bus & Tram Pass or discount added to your Oyster card, you can't lend it to someone else.
In conclusion, the main difference between Standard and Visitor Oyster cards is that Standard Oyster cards are reusable, while Visitor Oyster cards are disposable. In addition, standard Oyster cards do not come with a daily price cap, while Visitor Oyster cards do.
If you stop using the card altogether, there's a chance that your account will be closed (typically after at least 12 months of inactivity). This will appear on your credit report and could drop your score, so it's vital to keep your account active and make the payments needed to keep your account in good standing.