Is this a good time?
Recalling is something every hero can and will do multiple times in every game everywhere from the lowest elo to the world championships. Formerly known as "blue-pilling" because it used to be a consumable item (reference to the Matrix), it's often used. Why? Usually because a hero is either low in health, mana, or has too much gold and wants to buy some items. In some situations it's also used to escape certain death or to defend your base.
But are all recalls built equally? No. Recalling is an art that few have mastered, myself included. But by watching streams and through many games of experience, I can tell you a few tricks that I've picked up along the way.
General Recalling Strategies:
Problem: You never want to recall when your creeps are at your tower unless you're in danger of being dived. The reason for this is that towers kill enemy creeps much quicker than in lane. This means that you and your team are losing out on valuable cs. Even if your jungler is covering, this means that he's not jungling or ganking, which means an overall loss of gold for your team.
Remedy: Always try to push your lane to your opponent's turret before recalling, even if you have to burst several spells and expend most of your mana to do it.
Problem: Your opponent just did the above to your lane and has just recalled back to their base.
Remedy: You need to get as much cs off of the tower as possible and recall asap. The reason for this is that when your laning opponent comes back, he'll have lots of pretty new items which will make your laning phase extremely painful. He'll probably also have the ability to outpush you to your tower, which will lead to an overall loss in gold and thus lead to your team losing by a little. If the enemy jungler comes to push your tower, your jungler will need to cover.
Bot Lane Recalling:
Problem: Bot lane has a special strategy for recalling that the others don't simply because it's a duo lane. This means that if one person recalls and the other doesn't, a 1v2 could become very deadly very fast. For example, against a Sona/Alistar/Taric support lane, if either the support or the ad carry are left alone, they'll most likely be either denied cs or get killed.
Remedy: In the current meta with the high sustain lanes, you should both generally go back when your support has enough to buy philosopher's stone (620 gold) since the longer you have it, the more effective it becomes. Generally by this time the AD carry should have berzerker's greaves and probably another doran's blade if you've been farming well. However, don't forget to try and push your lane as far as safely possible first in order to miss out on the least amount of farm. If your AD carry stays, he might squeak out some extra cs, but it won't be nearly as easy or safe.
Conclusion: Just like in a NASCAR race, pitstops are vital in the charge to the nexus. However, the timing, speed, and efficiency of your recalls can make or break a game. Not recalling for a long time might give you some extra gold in the short run, but the possible penalties are high. Meanwhile, making pitstops at the wrong time might just cost you the race.