Parking is only good for type-in domains where people actually type your domain name or web address directly into the address bar. You need a really good keyword domain name to receive any kind of type-in traffic.
And by parking your domain names with the usual companies, sedo, domainsponsor, parked, etc. your domain name will get de-indexed and it will make it harder to get any significant search engine traffic to the domain name in the future.
Parking should be your last resort.