There's several advantages of using this method. But first of all let's start with the mix and supplies needed.
I've had great success direct planting cuttings straight into pots. But when you're limited on space and do not want to waste more soil than necessary into an entire pot, especially when you're using HP Promix, which is not the cheapest medium out there. Using the bag method seems to be the best idea.
I love HP promix, but at $39 for 3CU Ft it can get pricey and it's not always available year around at the local nurseries.
HP Promix ingredients:
• Canadian Sphagnum Peat Moss (65-75%)
• Perlite - horticultural grade
• Dolomitic and Calcitic limestone (pH adjuster)
• Wetting Agent
• MYCORRHIZAE™ mycorrhizal inoculum (Glomus intraradices)
So I've created my own mix using the cheaper peat moss bags. at $11 for 3cuft and a giant perlite bag at $17 for 4cuft. + A box of Mycorrhizae $25 that will last for a long time. You only need a few teaspoons of the Mycorrhizae per batch.
https://www.amazon.com/Xtreme-Gardening-4402-Mykos-2-2-Pound/dp/B003STB5N6/ref=sr_1_3?ie=UTF8&qid=1516816149&sr=8-3&keywords=mycorrhizae
So for about $30 I can make about 7cuft of mix.
My Mix:
Peat moss - 65%
Perlite - 35%
Mycorrhizae - 2 spoon full mixed in water.
Works just as well. I left out the lime because the cuttings don't need it until they get up potted.
I got my 4x16 Uline bags from EBay
https://www.ebay.com/itm/100-1000-4x16-Clear-1Mil-Poly-Bags-Plastic-Packaging-Baggies/221307916410?ssPageName=STRK%3AMEBIDX%3AIT&var=520187725633&_trksid=p2055119.m1438.l2649
Anyhow I really like this method because it has so many benefits.
1. Space - you can fit so many more of these bags in a bin compared to cups
2. Fungus Gnats - I do not cut holes in my bags instead I using a toothpick to aerate it, leaving no open area for the fungus gnats to get into
3. Moisture control - If you have the medium moist and not dripping wet the bags will not dry out as quickly
4. The length of the bags make so that a humidity bin is not necessary, just tape the opening at the top
There's a million ways to root figs this just another. I hope you find it useful.
How to up pot.