The drip rate regulates the amount of sending on the very first step in the campaign. For example: You added 1000 contacts in the campaign with the drip rate of 25, every day the sending of the campaign will start with 25 prospects and later it will proceed automatically.
We recommend to keep the drip rate at around 25 for LinkedIn and at around 30 for email because large amounts of sendings have chances of your LinkedIn account getting disconnected (for LinkedIn actions) or potentially being marked as a spammer (for mailing actions).
Please note : We give our recommendation more strongly for LinkedIn than for email.