I think the first question is going to be - what are you hoping to use it for?

I ask because some mixes are pretty much 'sterile' already, and perform just fine. However, even though many people apply the term 'sterile' to planting mediums, it should be noted - just for accuracy's sake - that it's almost impossible to sterilize soil without extremely harsh chemicals, or equipment not available to the average person. The closest that the average person can come is sanitization, and to keep it that way is next to impossible.

Many products used to create mixes are - barring contamination - pretty much 'sterile'. Vermiculite and perlite are examples.

Another issue that your post addresses is this issue of mycorrhizae. Now, it's true that some plants can form symbiotic relationships of this type, and there's no doubt that fungi (as well as other soil life forms) do play an integral role in the cycles that affect plant growth in nature, but these relationships are not necessary at all. This is why I asked about what will be your use of the potting soil. If it's for container plants, don't sweat the issue. There's a lot of hype surrounding mycorrhizae because it's one of those new products for which companies are trying to establish a market. Plants have been growing in containers for millennia. No special products necessary. This isn't to say that some things help more than others, it's to say that spores are EVERYWHERE! Wait... you just breathed in a thousand of them lol.

If you want to grow a tropical plant, for example, then odds are that any mycorrhizae that have a relationship with that plant will only thrive in the tropics. The products that are sold as mycorrhizae only contain a few species, and doubtfully those for tropical plants.

So... 'sterilization' of soil is really only important for those people who don't want to introduce bugs or diseases. And if you haven't experienced these problems, it's not really an issue. If you are running a commercial operation, and you want a good reputation, then finding a 'sterile' (sanitized) mix may be more important to you.

Various annuals and perennials. I'm planting lavender, stock (matthiola), and zinnias. On the site that I ordered the lavender seeds from, they don't recommend sowing them directly into the garden, and my soil is pretty sandy, so direct sowing into that would be extremely challenging. The lavender will eventually go into the garden. I haven't decided whether I'm going to put the zinnias and stock in or keep them in containers.

I make sure I de-sterilize it by adding soil where plants were growing.

If you are worried about damping off killing your seedlings - I have used some peroxide mixed in water in a spray b bottle with good luck.

To sterilize you can use a microwave, oven, or even better an old gas grill. Be sure to add some moisture before.

What gardengal said. Diseases are usually only a problem with tiny seedlings, so seed sprouting mixes are often 'sterile'. I use that in quotes because nothing really gets completely sterile, just close enough that it works.

Other than that, there's no real need IMO. Plants need the soil food web.