The fan grip trades speed for control: finger position, when it fits, how the disc lands softer, plus common mistakes, evidence and care for elbow and shoulder.
The honest answer: the fan grip is not a beginner grip born of weakness, but a control grip for throws where maximum spin doesn't matter. A retailer blog says that with the fan grip the disc lands softly and tends to stay where it lands, while with the power grip it skips or rolls further [1]. If you want to keep the same flight path but change the rolling after landing, you can switch grips [1].
A handout from the Graz disc golf club describes a different grip for shorter distances than for long ones: the index finger can lie on or under the outer rim [2]. The shorter the throw, the less you reach back and the "rounder" you throw [2]. That fits the fan grip, but is no proof that both mean the same thing.
How hard is it? The grip itself is easy; the art is knowing when to use it. There is no timeline. So don't practise the grip alone but the grip combined with distance: a grip you can only do in the garden won't help you on the course.
The fan grip fits when the disc should land softly and stay there: upshots, short drives, tight fairways [1]. For long drives you use the power grip, with the fingers firmly under the rim [2]. A study on the thumb shows that grip placement measurably changes speed and spin [3]. So this is in your hand.
Milestone: You can explain to a teammate in one sentence when you use which grip.
In the fan grip the fingers are spread under the disc instead of clamped against the edge (practice; the sources I read don't describe the finger position in detail). The Graz handout names the index finger on or under the rim for shorter throws and, for putts, the middle finger toward the disc centre to support the disc from below [2].
Milestone: Your disc sits securely in the hand without wobbling.
The shorter the distance, the less you reach back and the "rounder" the whole arm throws [2]. You look more toward the target, and the arm swings through less after release, for very short throws not at all [2].
Throw the same target with three speed levels and note where the disc lands. That is a practice idea, not a rule. The value lies in the table: you learn how much speed brings how many metres.
Milestone: Ten throws, five of them within about 3 m of the target (practice measure, not a standard).
Watch how the disc lands: softly or skipping? Retailer blogs associate the fan grip with little ground play [1]. Your feel for this landing is the real result of the exercise.
If you waver between two grips, keep the flight path and change only the grip: then you see what changes in the landing [1]. That is the cleanest way to learn what the grip really does.
A grip in which the fingers are spread under the disc instead of clamped against the edge. It gives control and a softer landing, but less spin [1]. The sources I read describe the finger position only roughly, so have a coach show you the grip.
For upshots and short drives, when the disc shouldn't roll far [1]. For long throws you use the firmer power grip [2].
Because according to retailer blogs the fan grip brings less ground play [1]: the disc skips or rolls less. The sources I read don't explain exactly why. Try it with the same flight path and two grips.
Probably, because it gives less spin. Grip choice measurably changes speed and spin [3]. For more distance, a firm grip with a loose arm is the usual way [1]. The fan grip gains control instead.
Reachback in Disc Golf: Straight Back to Prepare Speed