Cabaiguán When you creating a new Site Collection in SharePoint Online using Admin interface you will see it asks you to provide two settings. i.e. Storage and Resource Quota.
For the resource quota many times this question comes about what are they and how does they get calculated. Resource quotas are used to limit the risk that sand-boxed custom code can have on your site collection quota i.e. CPU and Memory.
If you are using sandbox custom solutions then the resource quota will be used based on whatever amount of resources it will consume. If you do not have any sandbox solutions then increasing or decreasing the resource on your site collection should not have any performance issue.
Marc posted a really good blog post on how to manager your resources with Office 365.